tests: drivers: spi: spi_loopback: support numaker_m55m1

Add support for Nuvoton numaker board numaker_m55m1.

Signed-off-by: cyliang tw <cyliang@nuvoton.com>

Author: cyliangtw

tests/drivers/spi/spi_loopback/boards/numaker_m55m1.conf

@@ -0,0 +1 @@
+CONFIG_SPI_ASYNC=n

tests/drivers/spi/spi_loopback/boards/numaker_m55m1.overlay

@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
+&pinctrl {
+/* EVB's NU5: SS/CLK/MISO/MOSI */
+	spi2_default: spi2_default {
+		group0 {
+			pinmux = <PA11MFP_SPI2_SS>,
+				 <PA10MFP_SPI2_CLK>,
+				 <PA9MFP_SPI2_MISO>,
+				 <PA8MFP_SPI2_MOSI>;
+		};
+	};
+};
+
+&spi2 {
+	slow@0 {
+		compatible = "test-spi-loopback-slow";
+		reg = <0>;
+		spi-max-frequency = <DT_FREQ_K(500)>;
+	};
+	fast@0 {
+		compatible = "test-spi-loopback-fast";
+		reg = <0>;
+		spi-max-frequency = <DT_FREQ_M(16)>;
+	};
+	status = "okay";
+	pinctrl-0 = <&spi2_default>;
+	pinctrl-names = "default";
+};