drm/amd/display: Add common modes to analog displays without EDID

drm/amd/display: Add common modes to analog displays without EDID

When the EDID of an analog display is not available, we can't
know the possible modes supported by the display. However, we
still need to offer the user to select from a variety of common
modes. It will be up to the user to select the best one, though.

This is how it works on other operating systems as well as the
legacy display code path in amdgpu.

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>