Give a definition for SHA-512. Also some refactoring of hash macros.
Give a definition for SHA-512. Also some refactoring of hash macros.

Signed-off-by: Daira Hopwood <cd7d43d5556a38ce626d53826fddc46adc597539@jacaranda.org>

zcash/zips,zcash/zips,zcash/zips,zcash/zips