msm: kgsl: For a5xx set GPU in privileged mode during self programming

In self programing path for accessing privileged memory
GPU needs to be in privileged mode. Setting GPU in
privileged mode before accessing such memory and
reset it later.

Change-Id: I4522965b73fed9fb6b9a33f3c555d2398a176d55
Signed-off-by: Sunil Khatri <sunilkh@codeaurora.org>
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>