gpio: Add APM X-Gene standby GPIO controller driver

Driver for standby GPIO controller of APM X-Gene SoCs on arm64.

Signed-off-by: Y Vo <yvo@apm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 8dcd0bd..4187fcb 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -367,6 +367,14 @@
 	  the generic flash controller's address and data pins. Say yes
 	  here to enable the GFC GPIO functionality.
 
+config GPIO_XGENE_SB
+	tristate "APM X-Gene GPIO standby controller support"
+	depends on ARCH_XGENE && OF_GPIO
+	select GPIO_GENERIC
+	help
+	  This driver supports the GPIO block within the APM X-Gene
+	  Standby Domain. Say yes here to enable the GPIO functionality.
+
 config GPIO_XILINX
 	tristate "Xilinx GPIO support"
 	depends on OF_GPIO && (PPC_OF || MICROBLAZE || ARCH_ZYNQ || X86)