gpio: rdc321x needs to select MFD_CORE

Fix rdc321x-southbridge build:  GPIO_RDC321X needs to select
MFD_CORE so that the core is built at the same (or higher)
tristate level.

rdc321x-southbridge.c:(.devinit.text+0x6103): undefined reference to `mfd_add_devices'
rdc321x-southbridge.c:(.devexit.text+0xe5f): undefined reference to `mfd_remove_devices'
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc:	Florian Fainelli <florian@openwrt.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/gpio/Kconfig

@@ -292,6 +292,7 @@ config GPIO_TIMBERDALE
 config GPIO_RDC321X
 	tristate "RDC R-321x GPIO support"
 	depends on PCI && GPIOLIB
+	select MFD_CORE
 	select MFD_RDC321X
 	help
 	  Support for the RDC R321x SoC GPIOs over southbridge