Only the OpenBIOS and SLOF firmwares use the CHRP NVRAM layout.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20191231183216.6781-14-philmd@redhat.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>