tests: drivers: spi: spi_loopback: add stm32u3 boards overlays

add SPI loopback test overlays for Nucleo U385RG-Q board.

Signed-off-by: Khaoula Bidani <khaoula.bidani-ext@st.com>

Author: kbidani

tests/drivers/spi/spi_loopback/boards/nucleo_u385rg_q.overlay

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2025 STMicroelectronics
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&spi3 {
+	dmas = <&gpdma1 0 11 STM32_DMA_PERIPH_TX
+		&gpdma1 1 10 STM32_DMA_PERIPH_RX>;
+	dma-names = "tx", "rx";
+	slow@0 {
+		compatible = "test-spi-loopback-slow";
+		reg = <0>;
+		spi-max-frequency = <500000>;
+	};
+	fast@0 {
+		compatible = "test-spi-loopback-fast";
+		reg = <0>;
+		spi-max-frequency = <16000000>;
+	};
+};
+
+&gpdma1 {
+	status = "okay";
+};

tests/drivers/spi/spi_loopback/testcase.yaml

@@ -69,6 +69,7 @@ tests:
       - nucleo_h753zi
       - nucleo_h745zi_q/stm32h745xx/m4
       - nucleo_h745zi_q/stm32h745xx/m7
+      - nucleo_u385rg_q
       - stm32h573i_dk
       - stm32n6570_dk/stm32n657xx/sb
       - stm32u083c_dk
@@ -102,6 +103,7 @@ tests:
       - nucleo_h745zi_q/stm32h745xx/m4
       - nucleo_h745zi_q/stm32h745xx/m7
       - nucleo_l152re
+      - nucleo_u385rg_q
       - nucleo_wba55cg
       - nucleo_wb55rg
       - nucleo_wl55jc