Convert CONFIG_DA8XX_GPIO to Kconfig

This converts the following to Kconfig:
   CONFIG_DA8XX_GPIO

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 5699a71..5cd8b34 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -58,6 +58,11 @@
 	  may be dedicated as a general purpose I/O or be assigned to
 	  a function of an embedded peripheral.
 
+config DA8XX_GPIO
+	bool "DA8xx GPIO Driver"
+	help
+	  This driver supports the DA8xx GPIO controller
+
 config INTEL_BROADWELL_GPIO
 	bool "Intel Broadwell GPIO driver"
 	depends on DM