V4L/DVB (4791): Added autodetected flag to the saa7134_dev structure

In case the exact board type needs to be determined by probing
or evaluating the eeprom, this flag allows to still set the 
board type via the card=xx insmod option. 
This is an extract of a patch by Francis Barber.

Signed-off-by: Hartmut Hackmann <hartmut.hackmann@t-online.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>