msm: kgsl: Add a check before requesting GPU keepalive

When GMU is diabled then attempt to access gmu register
will throw warning. Fixed by adding conditional check.
When GMU disabled then warning was observed after gpu
keepalive call so adding conditional check for keep-
alive only.

Change-Id: Ie9ce6ab3bc62addf29d69a96c41227175eea3e12
Signed-off-by: Amit Kushwaha <kushwaha@codeaurora.org>