Add support for big endian crc32

[ghost]

This is copied from [1] with minor changes since no support is needed for reflected crcs, just big-endian and little-endian.

This is work towards fixing #191

[1] https://github.com/antonblanchard/crc32-vpmsum/

Signed-off-by: Alan Mock alan@alanmock.com

[ghost]

@tuliom thanks for the review. I think I have made all the requested changes.

[ghost]

@tuliom can you take another look at this? I'd like to get it merged before I move on to the next part.

[RajalakshmiSR]

LGTM. @RajalakshmiSR , any other comments?

I merged it, Thanks.