Convert CONFIG_KIRKWOOD_GPIO to Kconfig

This converts the following to Kconfig:
   CONFIG_KIRKWOOD_GPIO

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 40abc33..b41a755 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -177,6 +177,11 @@
 	help
 	  This driver supports CREG GPIOs on Synopsys HSDK SOC.
 
+config KIRKWOOD_GPIO
+	bool "Kirkwood GPIO driver"
+	help
+	  This drdiver supports GPIOs on Kirkwood platforms
+
 config LPC32XX_GPIO
 	bool "LPC32XX GPIO driver"
 	depends on DM