Support cisco-8000 smartswitch image build. (#20488)

### Why I did it
Support Cisco smart switch build.

Author: liushilongbuaa

Makefile

@@ -37,6 +37,9 @@ endif
 PLATFORM_PATH := platform/$(if $(PLATFORM),$(PLATFORM),$(CONFIGURED_PLATFORM))
 PLATFORM_CHECKOUT := platform/checkout
 PLATFORM_CHECKOUT_FILE := $(PLATFORM_CHECKOUT)/$(PLATFORM).ini
+ifeq ($(SMARTSWITCH),1)
+PLATFORM_CHECKOUT_FILE := $(PLATFORM_CHECKOUT)/$(PLATFORM)-smartswitch.ini
+endif
 PLATFORM_CHECKOUT_CMD := $(shell if [ -f $(PLATFORM_CHECKOUT_FILE) ]; then PLATFORM_PATH=$(PLATFORM_PATH) j2 $(PLATFORM_CHECKOUT)/template.j2 $(PLATFORM_CHECKOUT_FILE); fi)
 MAKE_WITH_RETRY := ./scripts/run_with_retry $(MAKE)
 

platform/checkout/cisco-8000-smartswitch.ini

@@ -0,0 +1,4 @@
+[module]
+repo=git@github.com:Cisco-8000-sonic/platform-cisco-8000.git
+ref=0.master.ss.0.3
+