drm/amd/display: Add missing encoder setup to DACnEncoderControl

drm/amd/display: Add missing encoder setup to DACnEncoderControl

Apparently the DAC encoder needs to be set up before use.
The BIOS parser in DC did not support this so I assumed it was
not necessary, but the DAC doesn't work without it on some GPUs.

Fixes: 69b29b894660 ("drm/amd/display: Hook up DAC to bios_parser_encoder_control")
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>