drm/msm: refine hdmi bridge implementation

This change fixes an unclocked hdmi register access while going
to suspend state.

When splash is enabled on HDMI interface & we are going to turn
on the hdmi bridge power. Context of sde_hdmi connector is found
to be NULL because connector was not initialized yet and we never
called sde_hdmi_core_enable which enables hpd clocks.

Now when going to suspend system would be calling clock unprepare
for clocks which were never enabled. Hence hdmi clock gets unbalanced
and resulted in unclocked access to one of the hdmi register during
disabling vblank.

Adding struct sde_hdmi as a member of struct sde_hdmi_bridge and remove
dependency on sde connector to get the hdmi display object.

Change-Id: If96324fd5152ab0e721dfd38e93a68321a615455
Signed-off-by: Camus Wong <camusw@codeaurora.org>
Signed-off-by: Rahul Sharma <rahsha@codeaurora.org>
Signed-off-by: Suprith Malligere Shankaregowda <supgow@codeaurora.org>