drm/amd/display: Disable common modes for eDP

[Why]
Common modes are added to eDP 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 eDP will enable the scaler by
default.

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

Reviewed-by: Roman Li <roman.li@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>