drm/amd/display: Fix passive dongle mistaken as active dongle in EDID emulation

[Why]
dongle_type is set during dongle connection but for passive dongles,
dongle_type is not set. If user starts with an active dongle and
then switches to a passive dongle, it will still report as an active
dongle. Trying to emulate the wrong connecter type results in display
not lighting up.

[How]
Set dpcd_caps.dongle_type for passive dongles in detect_dp().

Signed-off-by: Samson Tam <Samson.Tam@amd.com>
Reviewed-by: Joshua Aberback <Joshua.Aberback@amd.com>
Acked-by: Eryk Brol <eryk.brol@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>