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

The GPIO pins connected to the 4 Software Switches ("SOFT_SW", SW2) 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.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20210303132941.3938516-1-geert+renesas@glider.be

arch/arm/boot/dts/r8a7791-koelsch.dts

@@ -81,6 +81,9 @@ lbsc {
 	keyboard {
 		compatible = "gpio-keys";
 
+		pinctrl-0 = <&sw2_pins>;
+		pinctrl-names = "default";
+
 		key-1 {
 			gpios = <&gpio5 0 GPIO_ACTIVE_LOW>;
 			linux,code = <KEY_1>;
@@ -618,6 +621,11 @@ sound_clk_pins: sound_clk {
 		groups = "audio_clk_a";
 		function = "audio_clk";
 	};
+
+	sw2_pins: sw2 {
+		pins = "GP_5_0", "GP_5_1", "GP_5_2", "GP_5_3";
+		bias-pull-up;
+	};
 };
 
 &ether {