drm/amd/display: Set CRTC source for DAC using registers

drm/amd/display: Set CRTC source for DAC using registers

Apparently the VBIOS SelectCRTC_Source function overwrites
a few registers (such as FMT_*) which DC writes in a different
place, which can cause problems.

Instead of using the SelectCRTC_Source function from the
VBIOS, use the DAC_SOURCE_SELECT register directly, similarly
to how it is done for digital link encoders.

Fixes: 3be26d81b150 ("drm/amd/display: Support DAC in dce110_hwseq")
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Tested-by: Mauro Rossi <issor.oruam@gmail.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>