tests: drivers: spi: support spi_loopback for imx95_evk m7

Added support for spi_loopback for imx95_evk m7.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>

Author: yangbolu1991

tests/drivers/spi/spi_loopback/boards/imx95_evk_mimx9596_m7.conf

@@ -0,0 +1 @@
+CONFIG_SPI_LOOPBACK_MODE_LOOP=y

tests/drivers/spi/spi_loopback/boards/imx95_evk_mimx9596_m7.overlay

@@ -0,0 +1,18 @@
+/*
+ * Copyright 2025 NXP
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&lpspi1 {
+	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 = <1000000>;
+	};
+};