crypto: sm2 - Provide sm2_compute_z_digest when sm2 is disabled

When sm2 is disabled we need to provide an implementation of
sm2_compute_z_digest.

Fixes: e5221fa6a355 ("KEYS: asymmetric: Move sm2 code into x509_public_key")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202306231917.utO12sx8-lkp@intel.com/
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

KEYS: asymmetric: Move sm2 code into x509_public_key

The sm2 certificate requires a modified digest. Move the code
for the hashing from the signature verification path into the
code where we generate the digest.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto: sm2 - introduce OSCCA SM2 asymmetric cipher algorithm

This new module implement the SM2 public key algorithm. It was
published by State Encryption Management Bureau, China.
List of specifications for SM2 elliptic curve public key cryptography:

* GM/T 0003.1-2012
* GM/T 0003.2-2012
* GM/T 0003.3-2012
* GM/T 0003.4-2012
* GM/T 0003.5-2012

IETF: https://tools.ietf.org/html/draft-shen-sm2-ecdsa-02
oscca: http://www.oscca.gov.cn/sca/xxgk/2010-12/17/content_1002386.shtml
scctc: http://www.gmbz.org.cn/main/bzlb.html

Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Tested-by: Xufeng Zhang <yunbo.xufeng@linux.alibaba.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>