drm/msm: Add support for msm8x94

This change adds the MDP and HDMI support for msm8x94.
Note that HDMI PHY registers are not being accessed anymore from
the driver.

Signed-off-by: Stephane Viau <sviau@codeaurora.org>
[rename compatible s/8x94/8994/ since preference is to not trust the
marketing folks who invent chip #'s but instead name things after the
lead chip.. we should rename some 80XY to 89XY to standardize on the
lead chip but leave that for another patch.  Also, update dt bindings
doc]
Signed-off-by: Rob Clark <robdclark@gmail.com>