[nrf fromtree] tests: drivers: spi: Add support spi_loopback for ek_ra8p1

Add support test app spi_loopback for Renesas ek_ra8p1

Signed-off-by: Khoa Nguyen <[email protected]>
(cherry picked from commit c6f237e)

Author: khoa-nguyen-18

tests/drivers/spi/spi_loopback/boards/ek_ra8p1_r7ka8p1kflcac_cm85.conf

@@ -0,0 +1,6 @@
+# Copyright (c) 2025 Renesas Electronics Corporation
+# SPDX-License-Identifier: Apache-2.0
+
+CONFIG_SPI_LOOPBACK_MODE_LOOP=y
+CONFIG_SPI_B_INTERRUPT=y
+CONFIG_SPI_B_RA_DTC=y

tests/drivers/spi/spi_loopback/boards/ek_ra8p1_r7ka8p1kflcac_cm85.overlay

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2025 Renesas Electronics Corporation
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/dt-bindings/clock/ra_clock.h>
+
+&spi1 {
+	rx-dtc;
+	tx-dtc;
+
+	slow@0 {
+		compatible = "test-spi-loopback-slow";
+		reg = <0>;
+		spi-max-frequency = <2000000>;
+	};
+
+	fast@0 {
+		compatible = "test-spi-loopback-fast";
+		reg = <0>;
+		spi-max-frequency = <3000000>;
+	};
+};