Add PCIe Root Port driver for Xilinx PCIe NWL bridge IP.

[bhelgaas: wait for link like dw_pcie_wait_for_link(), simplify bitmap
error path, typos, whitespace, fold in Dan Carpenter's PTR_ERR() fix]
Signed-off-by: NBharat Kumar Gogada <bharatku@xilinx.com>
Signed-off-by: NRavi Kiran Gummaluri <rgummal@xilinx.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Reviewed-by: NMarc Zyngier <marc.zyngier@arm.com>
Acked-by: NRob Herring <robh@kernel.org>