drm/amd/display: Initialize DAC in DCE link encoder using VBIOS

drm/amd/display: Initialize DAC in DCE link encoder using VBIOS

The VBIOS DAC1EncoderControl() function can initialize the DAC,
by writing board-specific values to certain registers.
Call this at link encoder hardware initialization time similarly
to how the equivalent UNIPHYTransmitterControl initialization
is done.

This fixes DAC output on the Radeon HD 7790.

Also remove the ENCODER_CONTROL_SETUP enum from the
dac_encoder_control_prepare_params function which is actually
not a supported operation for DAC encoders.

Fixes: 0fbe321a93ce ("drm/amd/display: Implement DCE analog link encoders (v2)")
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Tested-by: Mauro Rossi <issor.oruam@gmail.com>
Suggested-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>