xtensa/PCI: convert to pci_scan_root_bus() for correct root bus resources

Convert from pci_scan_bus() to pci_scan_root_bus() and remove root bus
fixups.  This fixes the problem of "early" and "header" quirks
seeing incorrect root bus resources.

This arch was unusual because it filled in bus->resource[0..3] in
pcibios_init(), then overwrote them, applied io_space.offset and
checked for unset resources in pcibios_fixup_bus().  I moved all of
that to a new pci_controller_apertures() that we can use before
scanning the root bus.

CC: Chris Zankel <chris@zankel.net>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>