media: imx: Unstage the imx7-media-csi driver

The imx7-media-csi driver, currently in staging, is ready for
prime-time. The staging TODO file lists a few items specific to that
driver, that are already addressed (the "all of the above" part) or can
be addressed later:

- The frame interval monitoring support is a software mechanism to
  monitor the device for unexpected stalls, and should be part of the
  V4L2 core if desired.

- Restricting the support media bus formats based on the SoC integration
  only aims at reducing userspace confusion by not enumerating options
  that are known not to be possible, it won't cause regressions if
  handled later.

Move the description of the media bus format restriction TODO item to
the driver, drop the other TODO items, and move the driver out of
staging.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>