boot: zephyr: boards: Assign boot_partition to code-patition

Use the boot_partition as the code-partition for RPI Pico W in order for
SysBuild to use the correct partition during the build process.

Signed-off-by: John Lin <john.lin@beechwoods.com>

Author: jlbwoods

boot/zephyr/boards/rpi_pico_rp2040_w.overlay

@@ -0,0 +1,11 @@
+/*
+ * Copyright (c) 2025 Beechwoods Software Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	chosen {
+		zephyr,code-partition = &boot_partition;
+	};
+};