PCI: Let pcibios_root_bridge_prepare() access bridge->windows

PCI: Let pcibios_root_bridge_prepare() access bridge->windows

When pci_register_host_bridge() is called, bridge->windows are already
available. However these windows are being moved temporarily from there.

To let pcibios_root_bridge_prepare() have access to these windows, move the
windows movement after calling this function. This is useful for the MIPS
ralink mt7621 platform so it can set up I/O coherence units and avoid
custom MIPS code in the mt7621 PCIe controller driver.

Link: https://lore.kernel.org/r/20211207104924.21327-2-sergio.paracuellos@gmail.com
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>