drm/nouveau/kms: don't call drm_dp_cec_set_edid() on TMDS

RM complains very loudly at the aux transaction attempts.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230525003106.3853741-10-skeggsb@gmail.com