drm/i915: Call intel_dp_mst_resume() before resuming displays

Since we need MST devices ready before we try to resume displays,
calling this after intel_display_resume() can result in some issues with
various laptop docks where the monitor won't turn back on after
suspending the system.

This order was originally changed in

	commit e7d6f7d7 ("drm/i915: resume MST after reading back hw state")

In order to fix some unclaimed register errors, however the actual cause
of those has since been fixed.

CC: stable@vger.kernel.org
Signed-off-by: Lyude <cpaul@redhat.com>
[danvet: Resolve conflicts with locking changes.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>