MIPS: ath79: Use the IRQ based GPIO key driver for the buttons

Now that the GPIO driver support interrupts we don't need to poll the
buttons.
Signed-off-by: Alban Bedel <albeu@free.fr>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/15283/
Cc: linux-mips@linux-mips.org
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Antony Pavlov <antonynpavlov@gmail.com>
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

arch/mips/boot/dts/qca/ar9132_tl_wr1043nd_v1.dts

@@ -22,11 +22,10 @@ extosc: ref {
 	};
 
 	gpio-keys {
-		compatible = "gpio-keys-polled";
+		compatible = "gpio-keys";
 		#address-cells = <1>;
 		#size-cells = <0>;
 
-		poll-interval = <20>;
 		button@0 {
 			label = "reset";
 			linux,code = <KEY_RESTART>;

arch/mips/boot/dts/qca/ar9331_dpt_module.dts

@@ -29,11 +29,10 @@ system {
 		};
 	};
 
-	gpio-keys-polled {
-		compatible = "gpio-keys-polled";
+	gpio-keys {
+		compatible = "gpio-keys";
 		#address-cells = <1>;
 		#size-cells = <0>;
-		poll-interval = <100>;
 
 		button@0 {
 			label = "reset";

arch/mips/boot/dts/qca/ar9331_dragino_ms14.dts

@@ -47,11 +47,10 @@ system {
 		};
 	};
 
-	gpio-keys-polled {
-		compatible = "gpio-keys-polled";
+	gpio-keys {
+		compatible = "gpio-keys";
 		#address-cells = <1>;
 		#size-cells = <0>;
-		poll-interval = <100>;
 
 		button@0 {
 			label = "jumpstart";

arch/mips/boot/dts/qca/ar9331_omega.dts

@@ -29,11 +29,10 @@ system {
 		};
 	};
 
-	gpio-keys-polled {
-		compatible = "gpio-keys-polled";
+	gpio-keys {
+		compatible = "gpio-keys";
 		#address-cells = <1>;
 		#size-cells = <0>;
-		poll-interval = <100>;
 
 		button@0 {
 			label = "reset";

arch/mips/boot/dts/qca/ar9331_tl_mr3020.dts

@@ -47,11 +47,10 @@ led3g {
 		};
 	};
 
-	gpio-keys-polled {
-		compatible = "gpio-keys-polled";
+	gpio-keys {
+		compatible = "gpio-keys";
 		#address-cells = <1>;
 		#size-cells = <0>;
-		poll-interval = <100>;
 
 		button@0 {
 			label = "wps";