Fix build. Split mediaprovider from priv_app.

This CL was accidentally reverted a second time by commit:
cb5129f9.  Submit it for the third,
and final, time.

(cherry-pick of 5637587d
which was in AOSP and internal master but not stage-aosp-master)

Bug: 62102757
Test: Builds and boots.
Change-Id: I0394907e808c737422e644aec452baa3e777cf6f