hw: arm: Carry RSDP specific data through AcpiRsdpData

hw: arm: Carry RSDP specific data through AcpiRsdpData

That will allow us to generalize the ARM build_rsdp() routine to support
both legacy RSDP (The current i386 implementation) and extended RSDP
(The ARM implementation).

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>