staging: mt7621-dts: add gpio perst to pcie bindings node

Driver has been changed to use perts gpio reset instead of
perst builtin behaviour. Update device tree accordly.
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mt7621-dts/mt7621.dtsi

 #include <dt-bindings/interrupt-controller/mips-gic.h>
+#include <dt-bindings/gpio/gpio.h>
 
 / {
 	#address-cells = <1>;
@@ -468,6 +469,7 @@ pcie: pcie@1e140000 {
 		#address-cells = <3>;
 		#size-cells = <2>;
 
+		perst-gpio = <&gpio 19 GPIO_ACTIVE_HIGH>;
 		pinctrl-names = "default";
 		pinctrl-0 = <&pcie_pins>;