msm: kgsl: Wait for pending irqs completion in gmu suspend

Ensure that adreno irqs are done in gmu suspend to avoid
race with gmu_suspend() and adreno_irq_handler(). This will
fix un-clocked register access in the adreno_irq_handler()
if it races with gmu suspend path.

Change-Id: Idd16defdd2a86b511c7dd13fc0c8704b29c7ee18
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>