i2c: smbus: add DDR support for SPD

On my x05 laptop I got:
Memory type 0x12 not supported yet, not instantiating SPD

Adding the 0x12 case lead to a successful instantiated SPD AT24 EEPROM.
i801_smbus 0000:00:1f.3: SMBus using polling
i2c i2c-6: 2/2 memory slots populated (from DMI)
at24 6-0050: 256 byte spd EEPROM, read-only
i2c i2c-6: Successfully instantiated SPD at 0x50
at24 6-0051: 256 byte spd EEPROM, read-only

And then, I decoded it successfully via decode-dimms.

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>