integrity: Asymmetric digsig supports SM2-with-SM3 algorithm

Asymmetric digsig supports SM2-with-SM3 algorithm combination,
so that IMA can also verify SM2's signature data.

Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Tested-by: Xufeng Zhang <yunbo.xufeng@linux.alibaba.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: Vitaly Chikunov <vt@altlinux.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>