drm/amd/display: Disable common modes for LVDS

drm/amd/display: Disable common modes for LVDS

[Why]
Common modes are added to LVDS for compatibility in clone mode, but
not all panels support them.  Non-native modes were disabled in the past
but this caused problems because compositors didn't use scaling for non
native modes. Now non-native modes on LVDS will enable the scaler by
default.

[How]
Check the connector type.  If the connector is LVDS avoid adding common
modes.

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