V4L/DVB (5411): Use v4l_printk_ioctl for debug

Using v4l_printk_ioctl saves a lot of code duplication. Also moved a few
ioctl cases to another function, improving the ioctl grouping.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>