Support secp256r1

A registry user wanting to support multiple curves would need to check both, or have a flag identifying which.

Without FIL having the precompile, would need to support it via a library like https://gist.github.com/Vectorized/599b0d8a94d21bc74700eb1354e2f55c

There are some differences between these libraries and ecrecover
1. ecrecover returns an address (pk-hash)
2. these libraries and also 7212 and eip-7951 require you to pass the public key to the signature verification

So this will be a more complicated flow than secp256k1 unless we can find a library that recovers the public key.