media: staging/imx: update TODO

Update TODO file:

- Remove TODO info about the OV564x driver, while this still needs
  to be done (add a OV5642 driver or merge with OV5640 driver), it
  is not relevant here.

- Update TODO about methods for retrieving CSI bus config.

- Add some TODO's about OF graph parsing restrictions.

Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>