lib: Add rp2040 build files

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

lib/rp2040/hardware/structs/systick.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef _HARDWARE_STRUCTS_SYSTICK_H
+#define _HARDWARE_STRUCTS_SYSTICK_H
+
+#include "hardware/address_mapped.h"
+#include "hardware/regs/m0plus.h"
+
+typedef struct {
+    io_rw_32 csr;
+    io_rw_32 rvr;
+    io_rw_32 cvr;
+    io_ro_32 calib;
+} systick_hw_t;
+
+#define systick_hw ((systick_hw_t *const)(PPB_BASE + M0PLUS_SYST_CSR_OFFSET))
+
+#endif