i2c: piix4: Add support for AMD ML and CZ SMBus changes

commit 032f708bc4f6da868ec49dac48ddf3670d8035d3 upstream.

The locations of SMBus register base address and enablement bit are changed
from AMD ML, which need this patch to be supported.

Signed-off-by: Shane Huang <shane.huang@amd.com>
Reviewed-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
[bwh: Backported to 3.2:
 - Adjust context
 - Aux bus support is not included]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>