media: dvb CA docs: place undocumented data together with ioctls

Right now, the same undocumented structs are on two places:
at ca_data_types.rst and together with their ioctls.

Move them to just one place and use the standard way to
represent them.

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