qapi/qom: Add ObjectOptions for secret*, deprecate 'loaded'

qapi/qom: Add ObjectOptions for secret*, deprecate 'loaded'

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

The 'loaded' property doesn't seem to make sense as an external
interface: It is automatically set to true in ucc->complete, and
explicitly setting it to true earlier just means that additional options
will be silently ignored.

In other words, the 'loaded' property is useless. Mark it as deprecated
in the schema from the start.

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