ARM: dts: silk: Configure pull-up for SOFT_SW GPIO keys

The GPIO pins connected to the 4 Software Switches ("SOFT_SW", SW12) do
not have external pull-up resistors, but rely on internal pull-ups being
enabled.  Fortunately this is satisfied by the initial state of these
pins.

Make this explicit by enabling bias-pull-up, to remove the dependency on
initial state and/or boot loader configuration.

While at it, rename the surrounding device node from "gpio-keys" to
"keyboard", to comply with generic node name recommendations.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/45f38a5333feba9bea80efeb5a41a6c3f60deda2.1619785905.git.geert+renesas@glider.be

arch/arm/boot/dts/r8a7794-silk.dts

@@ -45,9 +45,12 @@ memory@40000000 {
 		reg = <0 0x40000000 0 0x40000000>;
 	};
 
-	gpio-keys {
+	keyboard {
 		compatible = "gpio-keys";
 
+		pinctrl-0 = <&keyboard_pins>;
+		pinctrl-names = "default";
+
 		key-3 {
 			gpios = <&gpio5 10 GPIO_ACTIVE_LOW>;
 			linux,code = <KEY_3>;
@@ -358,6 +361,11 @@ du1_pins: du1 {
 		function = "du1";
 	};
 
+	keyboard_pins: keyboard {
+		pins = "GP_3_9", "GP_3_10", "GP_3_11", "GP_3_12";
+		bias-pull-up;
+	};
+
 	ssi_pins: sound {
 		groups = "ssi0129_ctrl", "ssi0_data", "ssi1_data";
 		function = "ssi";