[media] v4l2-ioctl.c: introduce INFO_FL_CLEAR to replace switch

The switch statement that determines how much data should be copied from
userspace is replaced by a table lookup.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>