msm: kgsl: Add content protection for A430

Content protection protects secure context content (example: framebuffer)
from unsecured contexts. TSB (trusted steering block) hardware is
programmed to route the memory access from trusted and untrused contexts
accordingly. If an unsecured context tries to read/write data from a
secured context, the access will be denied by TSB.

When content protection is enabled:
a) Create a secure pagetable with 256MB virtual pool to map secure buffers.
   All the secure buffers created in user mode driver and mapped to kernel
   are mapped to this virtual pool.
b) Enable GPU secure mode when executing commands from secure context.
   This enables GPU to use secure pagetable and render to secure buffer.

Change-Id: Ic07d9461152159aa7db1bb527085b4bc02fdb0e7
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>