hw/arm/virt-acpi-build: pass AcpiMcfgInfo to build_mcfg()

hw/arm/virt-acpi-build: pass AcpiMcfgInfo to build_mcfg()

To build MCFG, two information is necessary:

    * bus number
    * base address

Abstract these two information to AcpiMcfgInfo so that build_mcfg and
build_mcfg_q35 will have the same declaration.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20190419003053.8260-5-richardw.yang@linux.intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>