drm/amd/display: Fix wrong resolution with DP/VGA adapter

drm/amd/display: Fix wrong resolution with DP/VGA adapter

[Why]
Hotplugging the VGA side of some DP/VGA adapters caused the display to
light up with the wrong (non-native) resolution.

This is caused by the adapter misbehaving by reporting the wrong number
of downstream ports when the VGA side is unplugged (reports 1 instead of
0), but only if the SINK_COUNT DPCD register is read more than once.

[How]
To work around the adapter behavior, remove the sink if link is
detected, but EDID cannot be read.

Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Ilya <Ilya.Bakoulin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>