msm: kgsl: Wait for dispatcher on adreno idle

When waiting for the adreno device to become idle wait for
the dispatcher to complete processing commands that are
already submitted to the ringbuffer and prevent dispatcher
from submitting more commands while a thread is waiting for
dispatcher to become idle. This is required to support mutiple
ringbuffers where it is not sufficient to just wait for current
ringbuffer to become idle. All ringbuffers need to be idle and
to do that dispatcher needs to run without submitting more
commands but retiring commands that have been submitted.

Change-Id: Idd36a8da3c230981476348682cd22aed6dab113c
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>