media: staging: media: imx: Kconfig: support VIDEO_IMX7_CSI for imx8m

As described in NXPs' linux tree, the imx8m SoC includes the same
CSI bridge hardware that is part of imx7d. We should be able to
use the "fsl,imx7-csi" driver for imx8m directly.

Since ipuv3 is not relevant for imx8m, move that dependency to
VIDEO_IMX_CSI. That makes VIDEO_IMX7_CSI available to support imx8m
too.

Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>