i2c: piix4: don't regress on bus names

The I2C bus names are supposed to be stable as they can be used by
userspace to uniquely identify a specific I2C bus. So restore the
original names for all legacy (pre-SB800) devices.

For SB800 devices and later, improve the names. "SDA" refers to the
serial data pin of each SMBus port, it's an implementation detail the
user doesn't need to know. Use "port" instead, which is easier to
understand.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Tested-by: Christian Fetzer <fetzer.ch@gmail.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>