drm/msm/dp: remove dp post_open call as callback notifier

Remove DP post open call during successive HPD handling
as part of notifier callback. DP callback notifier is already
notified via connect work queue therefore there is no need
to initialize post_open callback. Also, skip HDCP and Audio
enablement over DP during early bootsplash screen.
Anyways as part of normal boot sequence, HDCP and Audio
are enabled over DP.

Change-Id: I1e53024efd2c3f1c03d6b02d643b33d7cd7891c5
Signed-off-by: Shubham Talekar <quic_stalekar@quicinc.com>