drm/i915/bdw+: Replace list_del+list_add_tail with list_move_tail

Same effect for slightly less source code and resulting binary.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1452521321-4032-2-git-send-email-tvrtko.ursulin@linux.intel.com