drm/nouveau/disp/dp: generate supported link rates table at detect time

Replaces the static list used during link training with a table built
dynamically from the union of source and sink capabilities.

Preparation for adding support for HBR3, LTTPR and eDP 1.4 link rates.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://gitlab.freedesktop.org/drm/nouveau/-/merge_requests/17