msm: kgsl: Allow concurrent requests for oob_perfcntr

Currently we directly send all oob requests to gmu. This
creates timeout waiting for ack when a thread attempts
to do oob set for oob_perfcntr while it was already set
by another thread because gmu firmware does not send ack
to second thread. Add and a counter inside device mutex's
protection for oob_perfcntr requests so that we only send
first oob set and last oob clear requests to gmu.

Change-Id: I702e9f1c45ec5dd9a24822300a7810dd390f1c7e
Signed-off-by: Pranav Patel <pranavp@codeaurora.org>