build: Use only one Makefile for apps

- Use one common Makefile for all test device apps.
- Use a single copy of syscall.[Sh].
- Update docs for building.

hw/application_fpga/apps/reset_test/main.c

@@ -1,7 +1,11 @@
 // Copyright (C) 2022, 2023 - Tillitis AB
 // SPDX-License-Identifier: GPL-2.0-only
 
+#include <fw/tk1/proto.h>
+#include <fw/tk1/reset.h>
+#include <fw/tk1/syscall_num.h>
 #include <stdint.h>
+#include <syscall.h>
 #include <tkey/assert.h>
 #include <tkey/debug.h>
 #include <tkey/io.h>
@@ -9,11 +13,6 @@
 #include <tkey/lib.h>
 #include <tkey/tk1_mem.h>
 
-#include "../testapp/syscall.h"
-#include "../tk1/proto.h"
-#include "../tk1/reset.h"
-#include "../tk1/syscall_num.h"
-
 // Converts a single hex character to its integer value
 static uint8_t hex_char_to_byte(uint8_t c)
 {