msm: kgsl: Do required clock settings for SDM660 GPU

Enable retention of memory and periphery logics for
GPU core clock. If the setting is not done then GPU
might get stale data while switching from NAP to
ACTIVE and which leads to page faults or hangs.

Clock settings need to be handled by client drivers only
and hence do it in KGSL driver.

Change-Id: Iea3fd720e2a0eda9f6ee719177a8898bc2bd75e4
Signed-off-by: Rajesh Kemisetti <rajeshk@codeaurora.org>