drm/amd/display: Add DAC_LoadDetection to BIOS parser (v2)

drm/amd/display: Add DAC_LoadDetection to BIOS parser (v2)

DAC_LoadDetection can be used to determine whether something
is connected to an analog connector by determining if there is
an analog load. This causes visible flickering on displays, so
we only resort to using this when the connected display doesn't
have an EDID.

For reference, see the legacy display code:
amdgpu_atombios_encoder_dac_load_detect

v2:
Only clear corresponding bit from BIOS_SCRATCH_0.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>