samples: i2s: add nucleo u575 overlay & conf files

Adds Nucleo U575 overlay and config files

Signed-off-by: Mario Paja <mario.paja@zal.aero>

Author: mariopaja-zal

samples/drivers/i2s/output/boards/nucleo_u575zi_q.conf

@@ -0,0 +1 @@
+CONFIG_HEAP_MEM_POOL_SIZE=4192

samples/drivers/i2s/output/boards/nucleo_u575zi_q.overlay

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+/*
+ * Copyright (c) 2025 ZAL Zentrum für Angewandte Luftfahrtforschung GmbH
+ * Copyright (c) 2025 Mario Paja
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	aliases {
+		i2s-tx = &sai1_a;
+	};
+};
+
+&pll2 {
+	/* 44.1KHz (-0.03% Error) */
+	div-m = <1>;
+	mul-n = <79>;
+	div-q = <2>;
+	div-r = <2>;
+	div-p = <7>;
+	clocks = <&clk_msis>;
+	status = "okay";
+};
+
+&sai1_a {
+	pinctrl-0 = <&sai1_mclk_a_pe2 &sai1_sd_a_pe6
+		&sai1_fs_a_pe4 &sai1_sck_a_pe5>;
+	pinctrl-names = "default";
+	status = "okay";
+	mclk-enable;
+	mclk-div-enable;
+	dma-names = "tx";
+};