Adding tool support for RSA auth of Barebox

This includes:
  1. A tool to convert an openssl-generated public key to C code
     for verification of an RSA signature.
  2. A tool to sign Barebox images, pre-pending a header file with
     the necessary information for verifying the image.

Change-Id: If8861f4851e32ffd32e6536be7ccc7b13119fe61
7 files changed