Separate system_ext_mac_permissions.xml out of system sepolicy.

Bug: 137712473
Test: boot crosshatch
Test: Moving product sepolicy to system_ext and checks the file contents in
      /system_ext/etc/selinux are identical to previous contents in
      /product/etc/selinux.
Change-Id: I434e7f23a1ae7d01d084335783255330329c44e9
diff --git a/Android.mk b/Android.mk
index f8b6803..9d04e93 100644
--- a/Android.mk
+++ b/Android.mk
@@ -323,6 +323,7 @@
     system_ext_seapp_contexts \
     system_ext_service_contexts \
     system_ext_service_contexts_test \
+    system_ext_mac_permissions.xml \
     system_ext_mapping_file \
 
 endif