drm/amd/display: Default max bpc to 16 for eDP

[Why]
Some 10bit eDP panels don't lightup after we cap bpc to 8.

[How]
Set default max_bpc to 16 for edp connector type.

Signed-off-by: Roman Li <roman.li@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>