Move the au8522 state structure, as well as exposing functions needed by the
analog side of the demodulator into a common header file.

Thanks to Michael Krufky <mkrufky@linuxtv.org> and Steven Toth
<stoth@linuxtv.org> for providing sample hardware, engineering level support,
and testing.
Signed-off-by: NDevin Heitmueller <dheitmueller@linuxtv.org>
Signed-off-by: NMichael Krufky <mkrufky@linuxtv.org>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>