Update flex counters config for Arista-7060X6-64PE-C256S2 (#21362)

Why I did it
Arista-7060X6-64PE-C256S2 is missing flex counters configs.

Work item tracking
Microsoft ADO (number only):
How I did it
Update flex counters config for Arista-7060X6-64PE-C256S2

How to verify it
Test it locally on Arista-7060X6-64PE-C256S2.

device/arista/x86_64-arista_7060x6_64pe/Arista-7060X6-64PE-C256S2/th5-a7060x6-64pe.config.bcm

@@ -1907,14 +1907,25 @@ bcm_device:
     0:
         global:
             ftem_mem_entries: 65536
+            sai_stats_support_mask: 0
+            global_flexctr_ing_action_num_reserved: 20
+            global_flexctr_ing_pool_num_reserved: 8
+            global_flexctr_ing_op_profile_num_reserved: 20
+            global_flexctr_ing_group_num_reserved: 2
+            global_flexctr_egr_action_num_reserved: 8
+            global_flexctr_egr_pool_num_reserved: 5
+            global_flexctr_egr_op_profile_num_reserved: 10
+            global_flexctr_egr_group_num_reserved: 1
 ...
 ---
 device:
     0:
         # Per pipe flex counter configuration
         CTR_EFLEX_CONFIG:
-            CTR_ING_EFLEX_OPERMODE_PIPEUNIQUE: 0
-            CTR_EGR_EFLEX_OPERMODE_PIPEUNIQUE: 0
+            CTR_ING_EFLEX_OPERMODE_PIPEUNIQUE: 1
+            CTR_ING_EFLEX_OPERMODE_PIPE_INSTANCE_UNIQUE: 1
+            CTR_EGR_EFLEX_OPERMODE_PIPEUNIQUE: 1
+            CTR_EGR_EFLEX_OPERMODE_PIPE_INSTANCE_UNIQUE: 1
 
         # IFP mode
         FP_CONFIG: