Allow signature/privileged apps with ACCESS_MTP special access

Allow signature/privileged apps with ACCESS_MTP access to Android/ on
public volumes.

Test: manual
Bug: 175170478
Bug: 174347304
Change-Id: I02dd3b5d29f8d4f919d4304058c83f5533b96182
Merged-In: I02dd3b5d29f8d4f919d4304058c83f5533b96182
(cherry picked from commit 1e75a8729ff2076393237be6fe89ef53720b7943)
3 files changed