lib: Add rp2040 build files

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

lib/rp2040/hardware/structs/xosc.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef _HARDWARE_STRUCTS_XOSC_H
+#define _HARDWARE_STRUCTS_XOSC_H
+
+#include "hardware/address_mapped.h"
+#include "hardware/platform_defs.h"
+#include "hardware/regs/xosc.h"
+
+/// \tag::xosc_hw[]
+typedef struct {
+    io_rw_32 ctrl;
+    io_rw_32 status;
+    io_rw_32 dormant;
+    io_rw_32 startup;
+    io_rw_32 _reserved[3];
+    io_rw_32 count;
+} xosc_hw_t;
+
+#define xosc_hw ((xosc_hw_t *const)XOSC_BASE)
+/// \end::xosc_hw[]
+
+#endif