msm: kgsl: Add A6XX hooks for content protection.

Allow content protection to be enabled. This change adds
the hooks, but is still dependent on additional changes
to enable content protection.

Change-Id: I6d90b3f5d2d4b9608a19795fb4de8a12f86c167e
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>