Does not support math in RAM origin with address

[HaoboGu]

It's similar with #65.

flip-link reports:

error: linking with `flip-link` failed: exit status: 1
 ...
 = note: rust-lld: error: section '.data' will not fit in region 'RAM': overflowed by 116 bytes
          rust-lld: error: section '.bss' will not fit in region 'RAM': overflowed by 21964 bytes
          rust-lld: error: section '.uninit' will not fit in region 'RAM': overflowed by 22988 bytes
   

when using memory.x:

MEMORY
{
  /* nRF52832 s132 7.3.0 */
  FLASH : ORIGIN = 0x26000,    LENGTH = 0x80000 - 0x26000
  RAM : ORIGIN = 0x20007af8, LENGTH = 0x20010000 - 0x20007af8
}

But compiles with

MEMORY
{
  /* nRF52832 s132 7.3.0 */
  FLASH : ORIGIN = 0x26000,    LENGTH = 360K
  RAM : ORIGIN = 0x20007af8, LENGTH = 64K - 30K
}