V4L/DVB (3578): Make scart definitions easier to handle

For the new routing implementation it is easier if all the 'normal'
scart inputs (IN1-IN4) are consecutive.

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