drm/amd/display: add detect caps for edp

1. The caps detect sequence for edp is different from dp.
   Added separate function for edp.
2. Removed max_link_setting and replaced it with verified
   to avoid confusion.
3. Reverted sink count guard for edp powerdown as unnecessary
   with the changes above.

Signed-off-by: Roman Li <Roman.Li@amd.com>
Signed-off-by: Tony Cheng <tony.cheng@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>