drm/amd/display: Add a function for checking tmds mode

drm/amd/display: Add a function for checking tmds mode

[Why]
DVI is TMDS signal like HDMI but without audio.  Current signal check
does not correctly reflect DVI clock programming.

[How]
Define a new signal check for TMDS that includes DVI to HDMI TMDS
programming.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Chris Park <chris.park@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>