Move mtectrl to private

Because mtectrl is a system internal domain, and we don't need to expose
the type to vendor.

Bug: 206895651
Test: build and boot
Change-Id: Idb5c4a4c6f175e338722971944bf08ba99835476
Merged-In: Idb5c4a4c6f175e338722971944bf08ba99835476
5 files changed