Explicitly update permissions after pre-grants.

Up until now, the OS had been implicitly relying on the
scanAvailableAsecs() method kicked off by StorageManager to actually
update any pre-granted permissions.

This was uncovered as part of ripping out ASECs, so now we need to
explicitly update permissions after pre-grants have been applied.

Test: builds, boots, Camera permissions can be granted
Bug: 65544665
Change-Id: I51e6bc81d9cf40c681094ee6069bc84a2edefea3