drm/amd/display: Fix DCE LVDS handling

drm/amd/display: Fix DCE LVDS handling

LVDS does not use an HPD pin so it may be invalid.  Handle
this case correctly in link encoder creation.

Fixes: 7c8fb3b8e9ba ("drm/amd/display: Add hpd_source index check for DCE60/80/100/110/112/120 link encoders")
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/5012
Cc: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Cc: Roman Li <roman.li@amd.com>
Reviewed-by: Roman Li <roman.li@amd.com>
Reviewed-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>