drm/amd/display: allow set dp drive setting when stream is not present

drm/amd/display: allow set dp drive setting when stream is not present

[why]
There is a change previously to disallow DM to set dp drive setings when
stream is not present. The logic might not work well with DP PHY
complaince scenario with a PHY test fixture attachment. We need to make
the method allow DP link drive settings changes even without stream
attached to it.

[how]
revert back to previous code in set drive setting function then add an
empty link_resource structure, then assign link resource based on
current link resource if link resource is allocated to the current pipe.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Wayne Lin <Wayne.Lin@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>