drm/amd/display: Refactor DAC load detection, move to HWSS

drm/amd/display: Refactor DAC load detection, move to HWSS

Slightly refactor and simplify DAC load detection.
This prepares the code to be used for also executing DAC
load detection on external DP bridge encoders.

DAC load detection belongs better in the hardware sequencer
code because the implementation is HW dependent and not all
chips support the functionality. The code is cleaner when
link detection probably doesn't call the VBIOS directly.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>