drm/amd/display: enable single dp seamless boot

[why]
seamless boot didn't work for non edp's before

[how]
removed edp-specific code, made dp read uefi-set link settings. Also fixed
a hubbub code line to be consistent with usage of function.

Signed-off-by: Martin Leung <martin.leung@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>