This adds a QAPI schema for the properties of the cryptodev-* objects.

These interfaces have some questionable aspects (cryptodev-backend is
really an abstract base class without function, and the queues option
only makes sense for cryptodev-vhost-user), but as the goal is to
represent the existing interface in QAPI, leave these things in place.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>