gpio: Add MT7621 GPIO support

This patch adds GPIO support for the Mediatek MT7621 SoC, tested on
MT7688 (Gardena smart-gateway). The driver is loosly based on the
Linux kernel version.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
[fixed checkpatch.pl warnings: Prefer 'unsigned int' to bare use of 'unsigned']
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 5cd8b34..35344e5 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -314,4 +314,12 @@
 	  Aside from the standard functions of input/output mode, and output
 	  value setting, the open-drain feature, which can configure individual
 	  GPIOs to work as open-drain outputs, is supported.
+
+config MT7621_GPIO
+	bool "MediaTek MT7621 GPIO driver"
+	depends on DM_GPIO && ARCH_MT7620
+	default y
+	help
+	  Say yes here to support MediaTek MT7621 compatible GPIOs.
+
 endmenu