[nrf fromlist] samples: drivers: spi_flash: Add nRF54H20DK support

Verified on nRF54H20DK, useful for testing external flash access.

Upstream PR: zephyrproject-rtos/zephyr#72519

Signed-off-by: Chaitanya Tata <[email protected]>

Author: krish2718

samples/drivers/spi_flash/boards/nrf54h20dk_nrf54h20_cpuapp.overlay

@@ -0,0 +1,16 @@
+/*
+ * Copyright (c) 2024 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&mx25uw63 {
+	status = "okay";
+};
+
+
+/ {
+	aliases {
+		spi-flash0 = &mx25uw63;
+	};
+};