drm/amd/display: Wait edp HPD to high in detect_sink

drm/amd/display: Wait edp HPD to high in detect_sink

[Why]
In 99% user case, edp will be post by vbios.
In 1% / current case: Lenovo don't light up edp panel in vbios
post stage, vbios won't be lit up. Thus in dal when we init DCN
10 hw, we power up edp, then we start detect_sink, but internal
time is too short, when we detect it, HPD is still low, so we don't
detect the edp, and edp shows black.

[How]
When we init hw, we wait edp HPD to high after power up edp.

Signed-off-by: Dale Zhao <dale.zhao@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>