crypto: ecdsa - Register NIST P521 and extend test suite

crypto: ecdsa - Register NIST P521 and extend test suite

Register NIST P521 as an akcipher and extend the testmgr with
NIST P521-specific test vectors.

Add a module alias so the module gets automatically loaded by the crypto
subsystem when the curve is needed.

Tested-by: Lukas Wunner <[email protected]>
Reviewed-by: Jarkko Sakkinen <[email protected]>
Signed-off-by: Stefan Berger <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>