Now we have two identical build_mcfg functions.

Consolidate them in acpi/pci.c.
Signed-off-by: NWei Yang <richardw.yang@linux.intel.com>

v4:
  * ACPI_PCI depends on both ACPI and PCI
  * rebase on latest master, adjust arm Kconfig
v3:
  * adjust changelog based on Igor's suggestion
Message-Id: <20190521062836.6541-2-richardw.yang@linux.intel.com>
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>