PCI: versatile: Add DT-based ARM Versatile PB PCIe host driver

This converts the Versatile PCI host code to a platform driver using the
commom DT parsing and setup.  The driver uses only an empty ARM
pci_sys_data struct and does not use pci_common_init_dev init function.
The old host code will be removed in a subsequent commit when Versatile is
completely converted to DT.

I've tested this on QEMU with the sym53c8xx driver in both i/o and memory
mapped modes.

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
CC: Russell King <linux@arm.linux.org.uk>
CC: Peter Maydell <peter.maydell@linaro.org>