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
3 files changed