ARM: brcmstb: Select ARCH_WANT_OPTIONAL_GPIOLIB

Select ARCH_WANT_OPTIONAL_GPIOLIB from BRCMSTB to allow GPIOLIB and
GPIO_BRCMSTB to be enabled.
Signed-off-by: Gregory Fong <gregory.0xf0@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

arch/arm/mach-bcm/Kconfig

@@ -145,6 +145,7 @@ config ARCH_BRCMSTB
 	select BRCMSTB_GISB_ARB
 	select BRCMSTB_L2_IRQ
 	select BCM7120_L2_IRQ
+	select ARCH_WANT_OPTIONAL_GPIOLIB
 	help
 	  Say Y if you intend to run the kernel on a Broadcom ARM-based STB
 	  chipset.