drm/msm: gpu: Use OPP tables if we can

If a OPP table is defined for the GPU device in the device tree use
that in lieu of the downstream style GPU frequency table. If we do
use the downstream table convert it to a OPP table so that we can
take advantage of the OPP lookup facilities later.

Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>