Add SM4 block cipher

[ChaoWeiAtGit]

SM4 (formerly SMS4)[1] is a block cipher used in the Chinese National Standard for Wireless LAN WAPI (Wired Authentication and Privacy Infrastructure). --from wikipedia

Checklist

• [ ] documentation is added or updated
• [x] tests are added or updated

[karel-m]

Just for record: standardisation of SM4 seems to got stuck https://tools.ietf.org/html/draft-ribose-cfrg-sm4-10

[hustliyilin]

Just for record: standardisation of SM4 seems to got stuck https://tools.ietf.org/html/draft-ribose-cfrg-sm4-10

@karel-m SM4 has become an ISO/IEC standard in 2021, see https://www.iso.org/standard/81564.html for details.

Besides, linux kernel and openssl also support SM4, so maybe this pr is suitable for libtom/libtomcrypt