gpio: atmel_pio4: Rework to support DM & DT

Rework the driver to support driver model and device tree, and
support to regard the pio4 pinctrl device as a child of
atmel_pio4 device.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 64cf221..8d9ab52 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -30,7 +30,7 @@
 
 config ATMEL_PIO4
 	bool "ATMEL PIO4 driver"
-	depends on DM
+	depends on DM_GPIO
 	default n
 	help
 	  Say yes here to support the Atmel PIO4 driver.