Add filesystem code and storage syscalls

Adds syscalls:

- ALLOCATE_AREA
- DEALLOCATE_AREA
- WRITE_DATA
- READ_DATA

and code to access the filesystem and the flash over SPI.

Based on original work by Daniel Jobson <jobson@tillitis.see> for
these files:

- auth_app.[ch]
- flash.[ch]
- spi.[ch]
- partition_table.[ch]
- rng.[ch]
- storage.[ch]

which are used with small changes to integrate with the new syscall
method.

Co-authored-by: Daniel Jobson <jobson@tillitis.se>
Co-authored-by: Mikael Ågren <mikael@tillitis.se>

hw/application_fpga/fw/tk1/rng.h

@@ -0,0 +1,11 @@
+// Copyright (C) 2024 - Tillitis AB
+// SPDX-License-Identifier: GPL-2.0-only
+#ifndef RNG_H
+#define RNG_H
+
+#include <stdint.h>
+
+uint32_t rng_get_word(void);
+uint32_t rng_xorwow(uint32_t state, uint32_t acc);
+
+#endif