boards: add dts and bindings for efm32pg23 and efm32pg28

Add device tree and support files for xg23 and xg28 dev Kit boards.

Signed-off-by: Christoph Jans <[email protected]>

Author: janchri

dts/arm/silabs/xg23/efm32pg23b310f512im48.dtsi

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2025 Christoph Jans
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <mem.h>
+#include <silabs/xg23/xg23.dtsi>
+
+/ {
+	sram0: memory@20000000 {
+		reg = <0x20000000 DT_SIZE_K(64)>;
+	};
+
+	soc {
+		compatible = "silabs,efm32pg23b310f512im48",
+					"silabs,efm32pg23",
+					"silabs,xg23",
+					"silabs,efm32",
+					"simple-bus";
+	};
+};
+
+&flash0 {
+	reg = <0x08000000 DT_SIZE_K(512)>;
+};

dts/arm/silabs/xg28/efm32pg28b310f1024im68.dtsi

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2025 Christoph Jans
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <mem.h>
+#include <silabs/xg28/xg28.dtsi>
+
+/ {
+	sram0: memory@20000000 {
+		reg = <0x20000000 DT_SIZE_K(256)>;
+	};
+
+	soc {
+		compatible = "silabs,efm32pg28b310f1024im68",
+					"silabs,efm32pg28",
+					"silabs,xg28",
+					"silabs,efm32",
+					"simple-bus";
+	};
+};
+
+&flash0 {
+	reg = <0x08000000 DT_SIZE_K(1024)>;
+};