media: cx25840: Register labeling, chip specific correction

Remove vbi_regs_offset from a group of registers that are 888 specific,
include those registers names. Sources used for reference are 885 and 888
datasheets.

Add labels to some undocumented registers.

Signed-off-by: Brad Love <brad@nextdimension.cc>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>