tools: Prune and document tools

Add a tools/README.md.

Remove:

- create_flash_image.py: role now overtaken by tkeyimage which does
  more.
- reset-tk1: Leftover from when production_test was removed.

Rename:

- makehex.py: Moved up one level.

hw/application_fpga/tools/makehex.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+#
+# This is free and unencumbered software released into the public domain.
+#
+# Anyone is free to copy, modify, publish, use, compile, sell, or
+# distribute this software, either in source code form or as a compiled
+# binary, for any purpose, commercial or non-commercial, and by any
+# means.
+
+from sys import argv
+
+binfile = argv[1]
+nwords = int(argv[2])
+
+with open(binfile, "rb") as f:
+    bindata = f.read()
+
+assert len(bindata) < 4*nwords
+assert len(bindata) % 4 == 0
+
+for i in range(nwords):
+    if i < len(bindata) // 4:
+        w = bindata[4*i : 4*i+4]
+        print("%02x%02x%02x%02x" % (w[3], w[2], w[1], w[0]))
+    else:
+        print("0")