media: intel/ipu6: Move isys_remove() close to isys_probe()

In preparation to fixing a leak in isys_probe(), move isys_remove().
The fix will introduce a new function that will also be called from
isys_remove(). The code needs to be rearranged to avoid a forward
declaration.

Having the .remove function close to the .probe function is also more
standard.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>