Enable the x509 parser to accept NIST P521 certificates and add the
OID for ansip521r1, which is the identifier for NIST P521.

Cc: David Howells <dhowells@redhat.com>
Tested-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>