x86/PCI: MMCONFIG: add resource to struct pci_mmcfg_region

This patch adds a resource and corresponding name to the MMCONFIG
structure.  This makes allocation simpler (we can allocate the
resource and name at the same time we allocate the pci_mmcfg_region),
and gives us a way to hang onto the resource after inserting it.
This will be needed so we can release and free it when hot-removing
a host bridge.

Reviewed-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>