drm/dp_mst: Factor out function to queue a topology probe work

Factor out a function to queue a work for probing the topology, also
used by the next patch.

Cc: Lyude Paul <lyude@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240722165503.2084999-2-imre.deak@intel.com