[MIPS] Kconfig fixes for BCM47XX platform

The patch below fixes two problems for Kconfig on the BCM47xx platform:

- arch/mips/bcm47xx/gpio.c uses ssb_extif_* functions. Selecting
  SSB_DRIVER_EXTIF makes sure those functions are available.
- arch/mips/pci/pci.c needs, when enabled, platform specific functions,
  which are defined when SSB_PCICORE_HOSTMODE is enabled.
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -59,6 +59,8 @@ config BCM47XX
 	select SYS_SUPPORTS_LITTLE_ENDIAN
 	select SSB
 	select SSB_DRIVER_MIPS
+	select SSB_DRIVER_EXTIF
+	select SSB_PCICORE_HOSTMODE if PCI
 	select GENERIC_GPIO
 	select SYS_HAS_EARLY_PRINTK
 	select CFE