msm: kgsl: Modify the a6xx interrupt mask for hwsched

With hardware scheduling, we only need to enable a subset
of interrupts as the rest of them are completely owned by
GMU.

Change-Id: I32afc4420299688b9a4322804ce972c79f1a7a22
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>