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/Makefile b/drivers/gpio/Makefile
index f186120..7ed9a4e 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -58,3 +58,4 @@
 obj-$(CONFIG_MSM_GPIO)		+= msm_gpio.o
 obj-$(CONFIG_$(SPL_)PCF8575_GPIO)	+= pcf8575_gpio.o
 obj-$(CONFIG_PM8916_GPIO)	+= pm8916_gpio.o
+obj-$(CONFIG_MT7621_GPIO)	+= mt7621_gpio.o