i2c: piix4: Add EFCH MMIO support to SMBus base address detect

The EFCH SMBus controller's base address is determined using details in
FCH::PM::DECODEEN[smbusasfiobase] and FCH::PM::DECODEEN[smbusasfioen].These
register fields were accessed using cd6h/cd7h port I/O. cd6h/cd7h port I/O
is no longer available in later AMD processors. Change base address
detection to use MMIO instead of port I/O cd6h/cd7h.

Signed-off-by: Terry Bowman <terry.bowman@amd.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>