msm: kgsl: Wake up gpu on kgsl_ioctl_timestamp_event only if necessary

Any call of kgsl_ioctl_timestamp_event wakes up gpu. In some cases
(like retired timestamp) it's not necessary. Wake up gpu only if it's
necessary.

Signed-off-by: Vladimir Razgulin <vrazguli@codeaurora.org>
Change-Id: I845faf6e9c6e4c9882a68489b64223919be3d21c