Reflect move of mapping file to /system.

Bug: 36783775
Test: boot device with matching sha256 and non-matching and verify that
device boots and uses either precompiled or compiled policy as needed. Also
verify that mapping_sepolicy.cil has moved.

(cherry-pick of commit: 39ffec77)
Change-Id: I9c3df2e7ed3f0eadd98e98529ebed360fec66dba