x86/PCI: use _CRS bus number aperture for host bridges from ACPI

Add the host bridge bus number aperture from _CRS to the resource list.
Like the MMIO and I/O port apertures, this will be used when assigning
resources to hot-added devices or in the case of conflicts.

Note that we always use the _CRS bus number aperture, even if we're
ignoring _CRS otherwise.

[bhelgaas: changelog]
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>