msm: kgsl: Enable A6XX content protection flag

To use secure memory allocations two things need to be setup:
1) The GPU has to be able to handle secure allocations.
2) The MMU has to be able to handle secure allocations.

Enable the ADRENO_CONTENT_PROTECTION flag to indicate
that the GPU is ready to handle secure allocations.

The device tree will control if the MMU is capable of handling
secure allocations and is not part of this patch.

Change-Id: Ic60ac3f95f9a45b1b79b3f9b68da6120c7489b46
Signed-off-by: Shrenuj Bansal <shrenujb@codeaurora.org>
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>