PCI: xilinx: Remove dependency on ARM-specific struct hw_pci

The Xilinx PCIe host controller driver uses pci_common_init_dev(), which
is ARM-specific and requires the ARM struct hw_pci.  The part of
pci_common_init_dev() that is needed is limited and can be done here
without using hw_pci.

Create and scan the root bus directly without using the ARM
pci_common_init_dev() interface.

[bhelgaas: revise changelog to show similarity to 79953dd2 ("PCI: rcar: Remove dependency on ARM-specific struct hw_pci")]
Signed-off-by: Bharat Kumar Gogada <bharatku@xilinx.com>
Signed-off-by: Ravi Kiran Gummaluri <rgummal@xilinx.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Michal Simek <michal.simek@xilinx.com>