7260cx3 DualToR config.bcm support based on DualToR setting in device metadata at boot time (#7168)

* 7260cx3 DualToR config.bcm support based on DualToR setting in device metadata at boot time. 
For HWSKU Arista-7260CX3-C64 the MMU setting SOC for T0/T1 is also combined into the config.bcm.j2 logic so use just one config file and adding delta based on Switch Roles.

Author: gechiang

device/arista/x86_64-arista_7260cx3_64/Arista-7260CX3-C64/th2-a7260cx3-64-64x100G-t0.config.bcm renamed to device/arista/x86_64-arista_7260cx3_64/Arista-7260CX3-C64/config.bcm.j2

@@ -1,3 +1,24 @@
+{# Construct config.bcm to include additional soc properties per specific device metadata requirement #}
+{%- set mmu_sock = 'mmu_init_config="MSFT-TH2-Tier1"' -%}
+{%- set IPinIP_sock = '' -%}
+{%- if DEVICE_METADATA is defined and DEVICE_METADATA['localhost'] is defined -%}
+{%-     if DEVICE_METADATA['localhost']['type'] is defined -%}
+{%-         set switch_role = DEVICE_METADATA['localhost']['type'] -%}
+{%-         if 'torrouter' in switch_role.lower() or 'torswitch' in switch_role.lower() %}
+{%-             set mmu_sock = 'mmu_init_config="MSFT-TH2-Tier0"' -%}
+{%-         endif %}
+{%-     endif %}
+{%-     if DEVICE_METADATA['localhost']['subtype'] is defined -%}
+{%-         set switch_subtype = DEVICE_METADATA['localhost']['subtype'] -%}
+{%-         if 'dualtor' in switch_subtype.lower() %}
+{%-             set IPinIP_sock = 'sai_tunnel_support=1
+                                   host_as_route_disable=1
+                                   l3_ecmp_levels=2' -%}
+{%-         endif %}
+{%-     endif %}
+{%- endif %}
+{# The following is the common soc properties that used to be named "th2-a7260cx3-64-64x100G-t1.config.bcm" #}
+
 PHY_AN_ALLOW_PLL_CHANGE=1
 arl_clean_timeout_usec=15000000
 asf_mem_profile=2
@@ -1012,4 +1033,5 @@ serdes_preemphasis_115=0x184606
 serdes_preemphasis_116=0x103706
 serdes_preemphasis_117=0x133c06
 
-mmu_init_config="MSFT-TH2-Tier0"
+{{ mmu_sock }}
+{{ IPinIP_sock }}

device/arista/x86_64-arista_7260cx3_64/Arista-7260CX3-C64/sai.profile

@@ -0,0 +1,2 @@
+SAI_INIT_CONFIG_FILE=/etc/sai.d/config.bcm
+SAI_NUM_ECMP_MEMBERS=64