V4L/DVB (5805): Bttv: Fix problems with probing for non-existent tuners

The bttv driver has code to detect if a tda9887 is present, that was previous
used to auto-load the tda9887 driver.  Now there is no tda9887 driver, so the
code is pointless; it just figures out if it should load the driver and then
does nothing.

For cards that are defined as having no tuner, the init code would still do
i2c probes for various tuner devices and auto-load the tuner module.  That can
be skipped for cards that don't need it.  The code is made to understand that
in addition to 'UNSET', 'TUNER_ABSENT' also means no tuner.

The tuner into printk()s are also made nicer.  Levels are added, INFO or
WARNING, depending on the meaning.  For cards with no tuner, or no tuner
defined, a more informative message is printed.

Card has no tuner, before patch:
bttv0: tuner type=-1
 or
bttv0: tuner type=4

After patch:

bttv0: tuner absent

Card has a tuner, but the type isn't defined, before patch:
bttv0: tuner type=-1

After patch:
bttv0: tuner type unset   [<- also warning now, as the tuner won't work right]

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>