gpio: atmel: Add the PIO4 driver support

The PIO4 is introduced from SAMA5D2, as a new version
for Atmel PIO controller.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index c58aa4d..fb4fd25 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -12,6 +12,7 @@
 obj-$(CONFIG_DM_GPIO)		+= gpio-uclass.o
 
 obj-$(CONFIG_AT91_GPIO)	+= at91_gpio.o
+obj-$(CONFIG_ATMEL_PIO4)	+= atmel_pio4.o
 obj-$(CONFIG_INTEL_ICH6_GPIO)	+= intel_ich6_gpio.o
 obj-$(CONFIG_KIRKWOOD_GPIO)	+= kw_gpio.o
 obj-$(CONFIG_KONA_GPIO)	+= kona_gpio.o