drm/amd/display: Use connector list for finding DPRX CRC aux

[Why]
This change is a refactor in preparation for adding locking and removing
the requirement for a stream state on the CRTC for enabling CRC capture
to fix igt@kms_plane_multiple@* warnings.

[How]
We can get the aux by finding the matching connector for the CRTC
with the assumption that we're not doing cloning.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: David Francis <David.Francis@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>