msm: kgsl: Remove the busy waiting loop from idle_check

Previously there were issues with extra long GPU sequences
running during the idle_check NAP attempt thwarting the
transition to NAP.  With the dispatcher architecture this
is much less likely to occur.  In addition the dispatcher
increases chances of a very short pause between a command
coming in and being submitted increasing the occurence of
"micro-NAPs" being caught by this loop.  These extremely
short NAP periods are actually a power loss on the CX rail.
Given that hw clock gating will take care of any long GPU
command tails remove the busy wait loop for power savings.

Change-Id: I4efc6215689c42ab03d4e478ad97839208d04004
Signed-off-by: Lucille Sylvester <lsylvest@codeaurora.org>