Allow to specify platform sepolicy dir mult. times

For automotive (and I assume for other verticals) it make sense to keep
vertical-specific policies outside of /system/sepolicy as those not used
by the phones. However, there's no way to do it rather than using
BOARD_PLAT_{PUBLIC|PRIVATE}_SEPOLICY_DIR build variables.

Bug: 70637118
Test: lunch device && m
Test: verify it builds, boots and logs seems to be reasonable
Test: enable full treble for aosp_car_x86 - verify it builds, boots and
no denials in the logs

Change-Id: Ia5fd847f7a6152ff6cf99bbbc12e1e322f7946ab
(cherry picked from commit 34f23364)

Android.mk

@@ -61,20 +61,12 @@ endif
 
 PLAT_PUBLIC_POLICY := $(LOCAL_PATH)/public
 ifneq ( ,$(BOARD_PLAT_PUBLIC_SEPOLICY_DIR))
-ifneq (1, $(words $(BOARD_PLAT_PUBLIC_SEPOLICY_DIR)))
-$(error BOARD_PLAT_PUBLIC_SEPOLICY_DIR must only contain one directory)
-else
 PLAT_PUBLIC_POLICY += $(BOARD_PLAT_PUBLIC_SEPOLICY_DIR)
 endif
-endif
 PLAT_PRIVATE_POLICY := $(LOCAL_PATH)/private
 ifneq ( ,$(BOARD_PLAT_PRIVATE_SEPOLICY_DIR))
-ifneq (1, $(words $(BOARD_PLAT_PRIVATE_SEPOLICY_DIR)))
-$(error BOARD_PLAT_PRIVATE_SEPOLICY_DIR must only contain one directory)
-else
 PLAT_PRIVATE_POLICY += $(BOARD_PLAT_PRIVATE_SEPOLICY_DIR)
 endif
-endif
 PLAT_VENDOR_POLICY := $(LOCAL_PATH)/vendor
 REQD_MASK_POLICY := $(LOCAL_PATH)/reqd_mask