SOFT: Check the EC Key on C_CreateObject and C_DeriveKey

When constructing an OpenSSL EC public or private key from PKCS#11
attributes or ECDH public data, check that the key is valid, i.e. that
the point is on the curve.

This prevents one from creating an EC key object via C_CreateObject with
invalid key data. It also prevents C_DeriveKey to derive a secret using
ECDH with an EC public key (public data) that uses a different curve
or is invalid by other means.

Signed-off-by: Ingo Franzki <ifranzki@linux.ibm.com>