V4L/DVB (8376): cx25840: move cx25840_vbi_setup to core.c and rename to cx25840_std_setup

cx25840_vbi_setup has nothing to do with setting up VBI, but everything
with setting up the standard. Move to cx25840-core.c and rename.

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