drm/amd/display: Allow embedded connectors without DDC

drm/amd/display: Allow embedded connectors without DDC

On some laptops, the embedded panel may not have
a DDC (display data channel) available. On these,
the EDID may be hardcoded in ACPI or the VBIOS.

In this case, use GPIO_DDC_LINE_UNKNOWN and don't fail.

Fixes: def3488eb0fd ("drm/amd/display: refactor HPD to increase flexibility")
Link: https://gitlab.freedesktop.org/drm/amd/-/work_items/5192
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>