V4L/DVB (3504): Medion 7134: Autodetect second bridge chip

The device, Medion 7134, has two saa7134 chips on it, but only one of them
is functional in the current saa7134 driver.
This patch adds autodetection for the second, unsupported saa7134 chip,
as SAA7134_BOARD_MD7134_BRIDGE_2, and displays a message to the user
(in dmesg) indicating that the second chip isn't yet functional.
This is useful for users, since two instances of the saa7134 driver
will spawn. This patch will prevent confusion by warning the user that
only one of the chips on the board are functional.
There are other versions of the SAA7134_BOARD_MD7134 with only a single
saa7134 bridge/decoder -- those devices will not be affected by this patch.
Only devices containing the second chip will display the warning.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>