drivers: thermal: Use high priority work queue for thermal processing

Thermal framework uses system freezable work queue for processing the
governor action and mitigation action will be performed in the same
context. System work queue can have one max active event processing
and if the mitigation action is delayed, that will bottleneck the
rest of the work queue event processing. This will result in delayed
action and temperature overshoot.

To avoid this, a new high priority thermal work queue is created and all
the passive monitoring will be done in the high priority context. Also
this work queue has a max active count defined as 16, which will allow
multi-processing of work events.

Change-Id: Id506f21c1583e0ba2e022f8b7bc28e3972c592ef
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>