drm/amd/display: get and restore link res map

[why]
When reboot the link res map should be persisted.  So during boot up,
driver will look at the map to determine which link should take priority
to use certain link res.  This is to ensure that link res remains
unshuffled after a reboot.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>