msm: kgsl: Make sure GPU is idle before changing the CPAPRIV bit

Add WAIT_FOR_IDLE and WAIT_FOR_ME/WAIT_FOR_CP_FLUSH commands before
adding commands to change the CPAPRIV bit. In absence of these
synchronizing commands write permission faults to pagetable_desc
are observed.

Change-Id: I1d47fd050a9d9f97858ee24b22a2a3cf99cc5e69
Signed-off-by: Puranam V G Tejaswi <pvgtejas@codeaurora.org>