Add support for parsing the parameters of a NIST P256 or NIST P192 key.
Enable signature verification using these keys. The new module is
enabled with CONFIG_ECDSA:
Elliptic Curve Digital Signature Algorithm (NIST P192, P256 etc.)
is A NIST cryptographic standard algorithm. Only signature verification
is implemented.

Cc: Herbert Xu
Cc: "David S. Miller"
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Stefan Berger
Signed-off-by: Herbert Xu