i2c-au1550: Add SMBus functionality flag

Add SMBus functionality flag, so we can use eeprom and similar
drivers.
Signed-off-by: Domen Puncer <domen.puncer@ultra.si>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>