tests: driver: spi: add overlay for xg23_rb4210a board

This patch introduces overlay for xg23_rb4210a for the spi_loopback
test. It is needed because it has another peripheral ip version than
all the other already tested board.

Signed-off-by: Martin Hoff <martin.hoff@silabs.com>

Author: Martinhoff-maker

tests/drivers/spi/spi_loopback/boards/xg23_rb4210a.conf

@@ -0,0 +1,2 @@
+CONFIG_DMA_MAX_DESCRIPTOR=16
+CONFIG_SPI_SILABS_EUSART_DMA_MAX_BLOCKS=10

tests/drivers/spi/spi_loopback/boards/xg23_rb4210a.overlay

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2025 Silicon Laboratories Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/dt-bindings/pinctrl/silabs/xg23-pinctrl.h>
+
+&eusart1 {
+	dmas = <&dma0 DMA_REQSEL_EUSART1TXFL>,
+	       <&dma0 DMA_REQSEL_EUSART1RXFL>;
+	dma-names = "tx", "rx";
+	#address-cells = <1>;
+	#size-cells = <0>;
+	pinctrl-0 = <&eusart1_default>;
+	pinctrl-names = "default";
+	status = "okay";
+	cs-gpios = <&gpioc 0 GPIO_ACTIVE_LOW>;
+
+	slow@0 {
+		compatible = "test-spi-loopback-slow";
+		reg = <0>;
+		spi-max-frequency = <500000>;
+	};
+
+	fast@1 {
+		compatible = "test-spi-loopback-fast";
+		reg = <1>;
+		spi-max-frequency = <10000000>;
+	};
+};
+
+&dma0 {
+	status = "okay";
+};

tests/drivers/spi/spi_loopback/testcase.yaml

@@ -341,6 +341,7 @@ tests:
   drivers.spi.silabs_s2.loopback.no_async:
     filter: CONFIG_SOC_FAMILY_SILABS_S2
     platform_allow:
+      - xg23_rb4210a
       - xg24_rb4187c
       - xg29_rb4412a
       - bg29_rb4420a
@@ -350,6 +351,7 @@ tests:
   drivers.spi.silabs_s2.loopback.dma.no_async:
     filter: CONFIG_SOC_FAMILY_SILABS_S2
     platform_allow:
+      - xg23_rb4210a
       - xg24_rb4187c
       - xg29_rb4412a
       - bg29_rb4420a