hw/pci: factor PCI reserve resources to a separate structure

hw/pci: factor PCI reserve resources to a separate structure

Factor "bus_reserve", "io_reserve", "mem_reserve", "pref32_reserve"
and "pref64_reserve" fields of the "GenPCIERootPort" structure out
to "PCIResReserve" structure, so that other PCI bridges can
reuse it to add resource reserve capability.

Signed-off-by: Jing Liu <jing2.liu@linux.intel.com>
Reviewed-by: Marcel Apfelbaum<marcel.apfelbaum@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>