msm: kgsl: Correct behavior of gpu_max_clock sysfs node

The legacy behavior of gpu_max_clock sysfs node is to update
thermal_pwrlevel instead of max_pwrlevel. Restore the legacy
behavior to avoid breaking entities using this sysfs node.
Also, ensure thermal limit set by devfreq cooling framework
and sysfs nodes like gpu_max_clock doesn't overwrite each other
and instead a consolidated limit based on limit set by both
entities is used as a final thermal limit.

Change-Id: I006786723d3e9c0deb29aec90b57eba8df1ec1d0
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>