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

The R-Car 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.

Note that the ARM pcibios functions expect the PCI sysdata to be a pointer
to a struct pci_sys_data.  Add a struct pci_sys_data as the first element
in struct gen_pci so that when we use a gen_pci pointer as sysdata, it is
also a pointer to a struct pci_sys_data.

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

Based on 499733e0 ("PCI: generic: Remove dependency on ARM-specific
struct hw_pci").

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>