msm: kgsl: call device->irqctrl from start/stop

These functions write registers and so if they are called
from kgsl_pwrctrl_irq() there is a chance that they
might be called when clocks are disabled.

Change-Id: I259d840d9996d424aba3e3481201d49f602637e8
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>