V4L/DVB: dib0700: break keytable into NEC and RC-5 variants

Instead of having one big keytable with 2 protocols inside, break it
into two separate tables, being one for NEC and another for RC-5 variants,
and properly identify what variant should be used at the boards entries.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>