msm: kgsl: Improve the idle_timeout

A slightly longer idle timeout is needed to ensure no edge UI cases
fall to SLEEP between frames.  With a 50ms timeout this can be seen
as stutter in a few cases on larger displays.  Increasing the value
to 80ms provides a reasonable buffer.

Change-Id: I19ba84e944d617252aed8bd323732ebc655e8462
Signed-off-by: Lucille Sylvester <lsylvest@codeaurora.org>