msm: kgsl: Secure buffer allocation for A430 content protection

Add support for secure buffer allocation for A430 content protection.
When GPU user mode driver requests kernel to allocate a secure buffer,
allocate the memory and call trustzone to restrict access for
allocated memory. Trustzone makes sure only GPU has access to this
memory. If restricted clients try to access this memory it will
trigger XPU violation.

Change-Id: I331e04fa0216837fb7394757bbeb326ec6b24e64
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>