MIPS: BMIPS: Enable ARCH_WANT_OPTIONAL_GPIOLIB

Allow BMIPS_GENERIC supported platforms to build GPIO controller
drivers.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Dragan Stancevic <dragan.stancevic@gmail.com>
Cc: cernekee@gmail.com
Cc: jaedon.shin@gmail.com
Cc: gregory.0xf0@gmail.com
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12019/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

Author: ffainelli

arch/mips/Kconfig

@@ -170,6 +170,7 @@ config BMIPS_GENERIC
 	select USB_EHCI_BIG_ENDIAN_MMIO if CPU_BIG_ENDIAN
 	select USB_OHCI_BIG_ENDIAN_DESC if CPU_BIG_ENDIAN
 	select USB_OHCI_BIG_ENDIAN_MMIO if CPU_BIG_ENDIAN
+	select ARCH_WANT_OPTIONAL_GPIOLIB
 	help
 	  Build a generic DT-based kernel image that boots on select
 	  BCM33xx cable modem chips, BCM63xx DSL chips, and BCM7xxx set-top