beckham: Update sepolicy for MotoMods

* Make policy less generic and more specific to what we are
  defining. Move ModService to mods_app and define the attribute
  in public policy so it can be properly used across system
  vendor split within private and vendor policies.

* Address mods_camd denials observed in logs

* Add seinfo for ModService app

* Allow ModService to read ro.boot.secure_hardware property

Change-Id: I1bffe7e7b1ceb54bd91ce3f8b982cf94d9afe2ab
Signed-off-by: Joshua Blanchard <joshua.lee.bbg@gmail.com>