i2c-bfin-twi: Update the dependencies

Since only a few Blackfins lack TWI, just list them in a depends
statement.

Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Jean Delvare <khali@linux-fr.org>