PCIe info design doc (#553)

* Add pcieinfo check design(Azure#64)

* Update pcieinfo_design.md

change format

* Update pcieinfo_design.md

* Update pcieinfo_design.md

* Add the config file 

Add the config file format

doc/pcieinfo_design.md

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+## Motivation
+Add a PCIe Diag tool for SONiC. This tool including three commands    
+### Commands
+
+    show platform pcieinfo     -----> Show current device PCIe info
+    show platform pcieinfo -c  -----> Check whether the PCIe info is correct   
+    pcieutil pcie_generate     -----> Generate an PCIe info congfig file
+
+## Implementation 
+### show utility update
+New item under menu `platform` in `show/main.py`  
+It will execute `pcieutil [options]`command
+
+**Syntax**
+
+     show  platform pcieinfo         ---->  pcieutil pcie_show
+     show  platform pcieinfo --check ---->  pcieutil pcie_check
+     show  platform pcieinfo -c      ---->  pcieutil pcie_check
+
+
+### pcieutil utility
+New utility in `sonic-utilities/pcieutil/`  
+It will import device plugin `pcie_commonl.py` and print the output returned by different API functions  
+
+**Syntax:**
+
+    pcieutil pcie_show
+This command will show the current PCIe info of current device
+
+    pcieutil pcie_check
+This command will compare the pcie info it got currently with config file pcie.yaml
+
+    pcieutil pcie_generate
+This command will generate pcie.yaml which used to record the original pcie info,to avoid use it by mistake,this command can not be executed by `show platform pcieinfo` command,but you can use it alone
+
+**Common API**
+
+Location: `sonic_platform_base/sonic_pice/pcie_common.py`
+
+Function: This file is used to fulfill the main interfaces including functions
+
+* **get_pcie_device()**
+     * Return a list including current pcie info of the device;
+* **get_pcie_check()**
+    * Return a list including compare the result of comparison,if not found the config file pcie.yaml .it will raise a system erron and exit
+* **dump_conf_yaml()**
+    * To generate pcie.yaml which used to record the original pcie info
+
+**Config file**
+
+Location: `device/Platofrm/plugins/pcie.yaml`
+
+Function: This file is used to as a standard to distinguish the device PCIe info. for different platform, config file will locate in differnet path
+
+***Format***
+
+    - bus: '00'
+      dev: '00'
+      fn: '0'
+      id: 1f0c
+      name: 'Host bridge: Intel Corporation Atom processor C2000 SoC Transaction Router'
+    - bus: '00'
+      dev: '01'
+      fn: '0'
+      id: 1f10
+      name: 'PCI bridge: Intel Corporation Atom processor C2000 PCIe Root Port 1'
+    - bus: '00'
+      dev: '02'
+      fn: '0'
+      id: 1f11
+      name: 'PCI bridge: Intel Corporation Atom processor C2000 PCIe Root Port 2'
+    - bus: '00'
+      dev: '03'
+      fn: '0'
+      id: 1f12
+      name: 'PCI bridge: Intel Corporation Atom processor C2000 PCIe Root Port 3'
+    ......
+
+## Command Output
+
+    root@sonic:~# show platform pcieinfo
+    ==============================Display PCIe Device===============================
+    ......
+    bus:dev.fn 01:00.0 - dev_id=0xb960, Ethernet controller: Broadcom Limited Device b960
+    bus:dev.fn 01:00.1 - dev_id=0xb960, Ethernet controller: Broadcom Limited Device b960
+
+    root@sonic:~# show platform pcieinfo -c
+    ===============================PCIe Device Check================================
+    Error: [Errno 2] No such file or directory: '/usr/share/sonic/device/x86_64-cel_seastone-r0/plugins/pcie.yaml'
+    Not found config file, please add a config file manually, or generate it by running [pcieutil pcie_generate]
+
+    root@sonic:~# pcieutil pcie_generate
+    Are you sure to overwrite config file pcie.yaml with current pcie device info? [y/N]: y
+    generate config file pcie.yaml under path /usr/share/sonic/device/x86_64-cel_seastone-r0/plugins
+
+    root@sonic:~# show platform pcieinfo -c
+    ===============================PCIe Device Check================================
+    ......
+    PCI Device: Ethernet controller: Broadcom Limited Device b960 ------------------ [Passed]
+    PCI Device: Ethernet controller: Broadcom Limited Device b960 ------------------ [Passed]
+    PCIe Device Checking All Test ----------->>> PASSED
+
+    root@sonic:~# show platform pcieinfo -c
+    ===============================PCIe Device Check================================
+    ......
+    PCI Device: Ethernet controller: Broadcom Limited Device b960 ------------------ [Failed]
+    PCI Device: Ethernet controller: Broadcom Limited Device b960 ------------------ [Passed]
+    PCIe Device Checking All Test ----------->>> FAILED
+           
+
+## Open questions
+