msm8937-common: Add selinux/private/service_contexts.

This makes sure that the remaining binder services
for radio end up in plat_service_contexts.

That in turn allows us to enforce that servicemanager
will only serve services from plat_service_contexts
on FULL_TREBLE devices.

Bug: 36866029
Test: boot, verify radio services still work
Change-Id: Ib67b3a03e5599484c5c4fb27a0f323a37dd51636
Signed-off-by: Isaac Chen <isaacchen@isaacchen.cn>

board/sepolicy.mk

@@ -2,4 +2,7 @@ include device/qcom/sepolicy/sepolicy.mk
 
 # SELinux
 BOARD_SEPOLICY_DIRS += \
-    $(VENDOR_PATH)/sepolicy
+    $(VENDOR_PATH)/sepolicy/vendor
+
+BOARD_PLAT_PRIVATE_SEPOLICY_DIR += \
+    $(VENDOR_PATH)/sepolicy/private