Convert from pci_create_bus() to pci_create_root_bus().  This way the root
bus resources are correct immediately.  This fixes the problem of "early"
and "header" quirks seeing incorrect root bus resources.

We can't use pci_scan_root_bus() because, like x86, ACPI hotplug currently
requires pci_bus_add_devices() in a separate host bridge .start() method.

v2: fix compile error by using window resource pointer instead

CC: Tony Luck <tony.luck@intel.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>