consolidate smbus initialization for pc_piix, mips_malta and mips_fulong.

Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Huacai Chen <zltjiangshi@gmail.com>
Signed-off-by: NIsaku Yamahata <yamahata@valinux.co.jp>
Reviewed-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>