drm/msm/dp: employ bridge mechanism for display enable and disable

Currently the msm_dp_*** functions implement the same sequence which would
happen when drm_bridge is used. hence get rid of this intermediate layer
and align with the drm_bridge usage to avoid customized implementation.

Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>

Changes in v2:
-- revise commit text
-- rename dp_bridge to msm_dp_bridge
-- delete empty functions

Changes in v3:
-- replace kzalloc() with devm_kzalloc()
-- replace __dp_display_enable() with dp_display_enable()
-- replace __dp_display_disable() with dp_display_disable()

Changes in v4:
-- msm_dp_bridge_init() called from msm_dp_modeset_init() same as dsi

Changes in v5:
-- delete attach, mode_fixup and pre_enable from dp_bridge_ops

Changes in v6:
-- rebase on msm-next-plus-fixes branch

Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Link: https://lore.kernel.org/r/1638918933-2544-1-git-send-email-quic_khsieh@quicinc.com
Signed-off-by: Rob Clark <robdclark@chromium.org>