Upgrade SAI xgs version to 8.4.0.2 and migrate to DMZ (#14119)

Why I did it
Update SAI xgs version to 8.4.0.2 and migrate xgs to DMZ repo.

How I did it
Update SAI xgs version in sai.mk.

How to verify it
Run the SONiC and SAI test with the8.4 SAI release pipeline.

platform/broadcom/sai.mk

@@ -1,8 +1,9 @@
-LIBSAIBCM_XGS_VERSION = 7.1.111.1
+LIBSAIBCM_XGS_VERSION = 8.4.0.2
 LIBSAIBCM_DNX_VERSION = 7.1.111.1
-LIBSAIBCM_BRANCH_NAME = REL_7.0_SAI_1.11
-LIBSAIBCM_XGS_URL_PREFIX = "https://sonicstorage.blob.core.windows.net/public/sai/bcmsai/$(LIBSAIBCM_BRANCH_NAME)/$(LIBSAIBCM_XGS_VERSION)"
-LIBSAIBCM_DNX_URL_PREFIX = "https://sonicstorage.blob.core.windows.net/public/sai/bcmsai/$(LIBSAIBCM_BRANCH_NAME)/$(LIBSAIBCM_DNX_VERSION)"
+LIBSAIBCM_XGS_BRANCH_NAME = SAI_8.4.0_GA
+LIBSAIBCM_DNX_BRANCH_NAME = REL_7.0_SAI_1.11
+LIBSAIBCM_XGS_URL_PREFIX = "https://sonicstorage.blob.core.windows.net/public/sai/sai-broadcom/$(LIBSAIBCM_XGS_BRANCH_NAME)/$(LIBSAIBCM_XGS_VERSION)/xgs"
+LIBSAIBCM_DNX_URL_PREFIX = "https://sonicstorage.blob.core.windows.net/public/sai/bcmsai/$(LIBSAIBCM_DNX_BRANCH_NAME)/$(LIBSAIBCM_DNX_VERSION)"
 
 BRCM_XGS_SAI = libsaibcm_$(LIBSAIBCM_XGS_VERSION)_amd64.deb
 $(BRCM_XGS_SAI)_URL = "$(LIBSAIBCM_XGS_URL_PREFIX)/$(BRCM_XGS_SAI)"