msm: kgsl: Trigger preemption from preemption complete interrupt

If a high priority context submits while preemption to a lower context
is underway, then preemption to higher context is not  triggered until
either we get a GPU command complete interrupt or another workload
from the higher context is submitted. To avoid this latency,
trigger preemption from the preemption complete interrupt.

CRs-Fixed: 1058401
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>
Change-Id: I0a05df94e7bdd5daadfa0713371a595a06b7bda7