RSA: Add RSA key types

RSA: Add RSA key types

The support of restricted RSA key types (OAEP and PSS) was lacking, or
dependent on the presence of restriction parameters.  For example,
this means that even though an RSA-PSS key may have been generated, it
may appear as a plain unrestricted RSA key if parameters weren't
present (which is the case when default restriction parameters are
used)

To make it clearer what an RSA key is intended for, and avoid
depending in an EVP_PKEY, we introduce RSA key types.  This is done by
reserving a section of the RSA flags (4 bits, which allows a total of
16 different types).

This isn't terribly important for EVP_PKEY_ASN1_METHOD code, as that
has access to the wrapping EVP_PKEY.  This is very important for
provider code, which has no access to the wrapping EVP_PKEY.

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/11710)