ARM: dts: stm32: fix gpio-keys node on STM32 MCU boards

Fix following warning observed with "make dtbs_check W=1" command.
It concerns f429 eval and disco boards, f769 disco board.

Warning (unit_address_vs_reg): /gpio_keys/button@0: node has a unit name,
but no reg or ranges property
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

arch/arm/boot/dts/stm32429i-eval.dts

@@ -119,17 +119,15 @@ led-blue {
 		};
 	};
 
-	gpio_keys {
+	gpio-keys {
 		compatible = "gpio-keys";
-		#address-cells = <1>;
-		#size-cells = <0>;
 		autorepeat;
-		button@0 {
+		button-0 {
 			label = "Wake up";
 			linux,code = <KEY_WAKEUP>;
 			gpios = <&gpioa 0 0>;
 		};
-		button@1 {
+		button-1 {
 			label = "Tamper";
 			linux,code = <KEY_RESTART>;
 			gpios = <&gpioc 13 0>;

arch/arm/boot/dts/stm32746g-eval.dts

@@ -81,12 +81,10 @@ led-blue {
 		};
 	};
 
-	gpio_keys {
+	gpio-keys {
 		compatible = "gpio-keys";
-		#address-cells = <1>;
-		#size-cells = <0>;
 		autorepeat;
-		button@0 {
+		button-0 {
 			label = "Wake up";
 			linux,code = <KEY_WAKEUP>;
 			gpios = <&gpioc 13 0>;

arch/arm/boot/dts/stm32f429-disco.dts

@@ -81,12 +81,10 @@ led-green {
 		};
 	};
 
-	gpio_keys {
+	gpio-keys {
 		compatible = "gpio-keys";
-		#address-cells = <1>;
-		#size-cells = <0>;
 		autorepeat;
-		button@0 {
+		button-0 {
 			label = "User";
 			linux,code = <KEY_HOME>;
 			gpios = <&gpioa 0 0>;

arch/arm/boot/dts/stm32f469-disco.dts

@@ -104,12 +104,10 @@ led-blue {
 		};
 	};
 
-	gpio_keys {
+	gpio-keys {
 		compatible = "gpio-keys";
-		#address-cells = <1>;
-		#size-cells = <0>;
 		autorepeat;
-		button@0 {
+		button-0 {
 			label = "User";
 			linux,code = <KEY_WAKEUP>;
 			gpios = <&gpioa 0 GPIO_ACTIVE_HIGH>;

arch/arm/boot/dts/stm32f769-disco.dts

@@ -75,12 +75,10 @@ led-red {
 		};
 	};
 
-	gpio_keys {
+	gpio-keys {
 		compatible = "gpio-keys";
-		#address-cells = <1>;
-		#size-cells = <0>;
 		autorepeat;
-		button@0 {
+		button-0 {
 			label = "User";
 			linux,code = <KEY_HOME>;
 			gpios = <&gpioa 0 GPIO_ACTIVE_HIGH>;