msm: kgsl: Check the current interrupt status before power operations

Sometimes the core will go idle before the interrupt can be handled on
the GPU. If that happens then we could go to a lower power state before
cleaning up the pending interrupt and various entities that might be
waiting for it. Consider the current interrupt status when checking
for idle.

Change-Id: Idd43e56e0162a522e0929df83531aff94beadc19
Signed-off-by: Harsh Vardhan Dwivedi <hdwivedi@codeaurora.org>