[media] atomisp: Unify lut free logic

ISP2401 introduced a helper for this which we can use just as well on the
ISP2400 and remove some more noise differences.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>