[media] af9035: change dual mode boolean to bit field

For some reason there seems to be value	0x03 in eeprom for dual mode
(and 0x00 for single mode). Boolean is not always 1 bit wide - it
could be 8 bit wide too. Storing number 0x03 to boolean causes driver
to thing there is 4 tuners in some cases :o
Add also some comments regarding to eeprom.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>