drm/amd/display: Take emulated dc_sink into account for HDCP

[Why]
While updating the config of hdcp, we use the sink_singal type of the
dc_sink to decide the HDCP operation mode. However, it doesn't consider
the case when the sink is a emulated one.

[How]
Take dc_em_sink into account while updating HDCP config.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Aurabindo Jayamohanan Pillai <Aurabindo.Pillai@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>