crypto: Copy an AES (Rijndael) implementation into tree

We are going to want an implementation of AES so that we can run
publicly-provided test vectors of our EAX implementation.

qemu seem to have a version with a fairly convenient shape, so lift it
wholesale into our tree, from upstream qemu (their git commit
55616505876d6683130076b810a27c7889321560).

The files in this patch are _exactly_ as copied from that qemu tree,
so that we can separate out our own changes.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>