drm/imx: ipuv3-plane: request modeset if plane offsets changed

If the framebuffer pixel format is planar YUV and unchanged, but the U
or V plane offsets change, do not return an error, but request a modeset
instead.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Liu Ying <gnuiyl@gmail.com>