media: staging/imx: rearrange group id to take in account IPU

Some imx system do not have IPU, so prepare the imx media drivers to
support this kind of devices. Rename the group ids to include an _IPU_
prefix, add a new group id to support systems with only a CSI without
IPU, and also rename the create internal links to make it clear that
only systems with IPU have internal subdevices.

Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>