pci: Add PCIe Gen4 controller driver for NXP Layerscape SoCs

Add PCIe Gen4 driver for the NXP Layerscape SoCs. This PCIe
controller is based on the Mobiveil IP, which is compatible
with the PCI Express™ Base Specification, Revision 4.0.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: Bao Xiaowei <Xiaowei.Bao@nxp.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>