Rather than use strcasecmp() in the hash algorithm search, require the
caller to do this first. Most of U-Boot can use lower case anyway, and
the hash command can convert to lower case before calling hash_command().
This saves needing strcasecmp() for boards that use hashing but not
the hash command.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add the CRC32 algorithm to the list of available hashes, and make
the crc32 command use hash_command(). Add a new crc32_wd_buf() to
make this possible, which puts its result in a buffer rather than
returning it as a 32-bit value.

Note: For some boards the hash command is not enabled, neither
are sha1, sha256 or the verify option. In this case the full
hash implementation adds about 500 bytes of overhead. So as a
special case, we use #ifdef to select very simple bahaviour in
that case. The justification for this is that it is currently
a very common case (virtually all boards enable crc32 but only
some enable more advanced features).

Signed-off-by: Simon Glass <sjg@chromium.org>

Some hashing commands permit saving the hash in an environment variable,
and verifying a hash from there. But the crc32 command does not support
this. In order to permit crc32 to use the generic hashing infrastructure,
add a flag to select which behaviour to use.

Signed-off-by: Simon Glass <sjg@chromium.org>

We have a SHA1 command and want to add a SHA256 command also. Instead of
duplicating the code, create a generic hash API which can process
commands for different algorithms.

Signed-off-by: Simon Glass <sjg@chromium.org>