lib: Add rp2040 build files

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

lib/rp2040/hardware/structs/watchdog.h

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef _HARDWARE_STRUCTS_WATCHDOG_H
+#define _HARDWARE_STRUCTS_WATCHDOG_H
+
+#include "hardware/address_mapped.h"
+#include "hardware/platform_defs.h"
+#include "hardware/regs/watchdog.h"
+
+typedef struct {
+    io_rw_32 ctrl;
+    io_wo_32 load;
+    io_ro_32 reason;
+    io_rw_32 scratch[8];
+    io_rw_32 tick;
+} watchdog_hw_t;
+
+#define watchdog_hw ((watchdog_hw_t *const)WATCHDOG_BASE)
+
+#endif