gpio: add nexell driver

Changes in relation to FriendlyARM's U-Boot nanopi2-v2016.01:
- livetree API (dev_read_...) is used instead of fdt one (fdt...).

Signed-off-by: Stefan Bosch <stefan_b@posteo.net>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 0e8ad95..c192844 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -457,4 +457,13 @@
 	help
 	  Say yes here to support MediaTek MT7621 compatible GPIOs.
 
+config NX_GPIO
+	bool "Nexell GPIO driver"
+	depends on DM_GPIO
+	help
+	  Support GPIO access on Nexell SoCs. The GPIOs are arranged into
+	  a number of banks (different for each SoC type) each with 32 GPIOs.
+	  The GPIOs for a device are defined in the device tree with one node
+	  for each bank.
+
 endmenu