drm/amd/display: Set emulated sink type to HDMI accordingly.

[WHY & HOW]
Virtual sink is not audio-capable and this causes kms_hdmi_inject's
inject-audio to fail. Set it to HDMI according to EDID.

Reviewed-by: Chao-kai Wang <stylon.wang@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>