Implement SM2 support for OpenSSL backend

[andrey-utkin]

Description

Currently it fails to build.

Steps to Reproduce

1. Disable the rejection hardcoded in the build system.
2. cmake -DCRYPTO_BACKEND=openssl -DENABLE_SM2=On . && make && ctest

Expected Behavior

Builds and passes all tests.

Actual Behavior

Build failure.