PackageManager: Restrict system packages to protected storage

Don't allow packages signed with the platform key to be
installed into user (or app) controlled storage

(cherry-picked from 64fa8092090d067d78163b8ebce45baa1123ce9d
 with changed file path)

Patch set 2: Fix compile error due to changed function name

Change-Id: I7390b3bdf5289411f7a335c69635bed9f74bbfb3