update config options for crypto backend

[pabuhler]

Wrong things will happen if you enable two or more of --enable-openssl, --enable-wolfssl, and --enable-nss, and I think we have nothing that guards against this. This isn't a new problem with wolfssl (it was already a problem with just openssl and nss), but should we have something to protect against this?

Or possibly even change the configure option syntax to --enable-crypto=[openssl,wolfssl,nss] with the 3.0 release, since that's where we're putting other breaking changes.

Originally posted by @JonathanLennox in https://github.com/cisco/libsrtp/issues/692#issuecomment-2026406283