msm: kgsl: Decouple zap shader and content protection on a6x

The two features work independently from each other so decouple
them and we will not likely have any a6x targets without a secure
mmu.

Change-Id: I43f602b7a5f6b471b945c430976232808e5fdfc4
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>