eng_devcrypto: save ioctl if EVP_MD_..FLAG_ONESHOT

Since each ioctl causes a context switch, slowing things down, if
EVP_MD_CTX_FLAG_ONESHOT is set, then:
 - call the ioctl in digest_update, saving the result; and
 - just copy the result in digest_final, instead of using another ioctl.

Signed-off-by: Eneas U de Queiroz <cote2004-github@yahoo.com>

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7585)