Add ref counting and control how we allocate storage for the private key.
We will need this type in following commits where we move the ecx code
to be provider aware.
Reviewed-by: NPatrick Steuer <patrick.steuer@de.ibm.com>
Reviewed-by: NShane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/10964)