msm: kgsl: Avoid L2PC on masked CPUs

If any of the Graphics rendering threads are running
on masked CPUs, avoid L2PC for some duration on that
CPU. This reduces latency on CPU (latency mainly
because of L2 cache flush) and helps on performance.
This change uses pm_qos_update_request_timeout() API.

Add l2pc-cpu-mask property in device tree to enable
this.

CRs-Fixed: 962598
Change-Id: If90090cd2c68ea7c07e269723931fef7201ef136
Signed-off-by: Prakash Kamliya <pkamliya@codeaurora.org>

# Conflicts:
#	drivers/gpu/msm/kgsl_pwrctrl.c