Add support for devfreq to dynamically control the GPU frequency.
By default try to use the 'simple_ondemand' governor which can
adjust the frequency based on GPU load.

v2: Fix __aeabi_uldivmod issue from the 0 day bot and use
devfreq_recommended_opp() as suggested by Rob.
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>