mac_permissions: explicitly label all mac_permissions files

*mac_permissions.xml files need to be explicitly labeled as they are now split
cross system and vendor and won't have the generic world readable
'system_file' or 'rootfs' label.

Bug: 36003167
Test: no new 'mac_perms_file' denials at boot complete on sailfish
Test: successfully booted into recovery without denials and sideloaded
      OTA update.
Test: Launch 'chrome' and succesfully load a website.
Test: Launch Camera and take a picture.
Test: Launch Camera and record a video, succesfully playback recorded
      video

Change-Id: I1c882872bb78d1242ba273756ef0dc27487f58fc
Signed-off-by: Sandeep Patil <sspatil@google.com>