msm: kgsl: Increase events worker thread priority

Increase kgsl-events worker thread priority to run at high
priority among default worker threads to get some benefit
in fence signaling.

Change-Id: Ia3eeb1beabc4bca1ef69e37bc40ef9868e29572b
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>