This new command supports hashing SHA1 and SHA256. It could be extended
to others such as MD5 and the CRC algorithms. The syntax is modeled on
those:

   hash <algorithm> <address> <length> [*<dest_addr> | <dest_envvar>]

to calculate a hash, and:

   hash -v <algorithm> <address> <length> [*<verify_addr> | <verify_envvar>]

to verify a hash.

Use CONFIG_CMD_HASH to enable the command, CONFIG_SHA1 to enable SHA1 and
CONFIG_SHA256 to enable SHA256.

The existing sha1sum command remains.
Signed-off-by: NSimon Glass <sjg@chromium.org>