block: vhdx initial file create

Initial file create, and structure definitions from the
specification.

Note, this is an interim commit, and will be squashed and cleaned
up prior to upstream submission.
qemu: add castagnoli crc32c checksum algorithm

This adds the Castagnoli CRC32C algorithm, using the 0x11EDC6F41
polynomial.

This is extracted from the linux kernel cryptographic crc32.c module.

The algorithm is based on:

Castagnoli93: Guy Castagnoli and Stefan Braeuer and Martin Herrman
             "Optimization of Cyclic Redundancy-Check Codes with 24
              and 32 Parity Bits", IEEE Transactions on Communication,
              Volume 41, Number 6, June 1993