Hello,
Mbed TLS doesn't have arithmetic for arbitrary elliptic curves. Adding support for another curve requires extra code, not just the curve parameters.
There's a pull request for adding SM2 to Mbed TLS: https://github.com/ARMmbed/mbedtls/pull/4091 https://github.com/ARMmbed/mbedtls/pull/4091 . It looks close to complete, but isn't passing all tests and needs review.
Best regards,