boards: silabs: siwx91x: Add support for si7021 sensor

Report configuration of the Si7021 in the board definitions.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>

Author: jerome-pouiller

boards/silabs/radio_boards/siwx917_rb4338a/siwx917_rb4338a.dts

@@ -28,6 +28,7 @@
 		led1 = &led1;
 		sw0 = &button0;
 		sw1 = &button1;
+		dht0 = &si7021;
 	};
 
 	leds {
@@ -66,6 +67,12 @@
 			pinmux = <ULPUART_RX_ULP9>;
 		};
 	};
+
+	ulpi2c_default: ulpi2c_default {
+		group {
+			pinmux = <ULPI2C_SDA_ULP6>, <ULPI2C_SCL_ULP7>;
+		};
+	};
 };
 
 &ulpuart {
@@ -74,6 +81,18 @@
 	pinctrl-names = "default";
 };
 
+&ulpi2c {
+	status = "okay";
+	pinctrl-0 = <&ulpi2c_default>;
+	pinctrl-names = "default";
+	clock-frequency = <DT_FREQ_K(100)>;
+
+	si7021: si7021@40 {
+		compatible = "silabs,si7006";
+		reg = <0x40>;
+	};
+};
+
 &flash0 {
 	partitions {
 		compatible = "fixed-partitions";