sm8350-common: Switch to SYSTEM_EXT_{PUBLIC,PRIVATE}_SEPOLICY_DIRS

Fixes:
warning: BOARD_PLAT_PRIVATE_SEPOLICY_DIR has been deprecated.
    Use SYSTEM_EXT_PRIVATE_SEPOLICY_DIRS instead.
warning: BOARD_PLAT_PUBLIC_SEPOLICY_DIR has been deprecated.
    Use SYSTEM_EXT_PUBLIC_SEPOLICY_DIRS instead.
Change-Id: I752602079de8ff4c5370fe3ec861b8746838d878

BoardConfigCommon.mk

@@ -184,8 +184,8 @@ VENDOR_SECURITY_PATCH := 2021-10-01
 # Sepolicy
 include device/qcom/sepolicy_vndr/SEPolicy.mk
 
-BOARD_PLAT_PRIVATE_SEPOLICY_DIR += $(COMMON_PATH)/sepolicy/private
-BOARD_PLAT_PUBLIC_SEPOLICY_DIR += $(COMMON_PATH)/sepolicy/public
+SYSTEM_EXT_PRIVATE_SEPOLICY_DIRS += $(COMMON_PATH)/sepolicy/private
+SYSTEM_EXT_PUBLIC_SEPOLICY_DIRS += $(COMMON_PATH)/sepolicy/public
 BOARD_VENDOR_SEPOLICY_DIRS += $(COMMON_PATH)/sepolicy/vendor
 
 # Soong