drm/msm/hdmi: rework hdmi configurations, using dt_match[]

In the same idea mdp5_cfg was added, this change allows us to quickly
add new instances, such as apq8084's HDMI in this case.

Signed-off-by: Stephane Viau <sviau@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>