Add a sanity check on the length of pkeyutl inputs

When signing or verifying a file using pkeyutl the input is supposed to
be a hash. Some algorithms sanity check the length of the input, while
others don't and silently truncate. To avoid accidents we check that the
length of the input looks sane.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6284)