pci_ep: layerscape: Add the PCIe EP mode support for lx2160a-v2

Add the PCIe EP mode support for lx2160a-v2 platform.

Signed-off-by: Xiaowei Bao <xiaowei.bao@nxp.com>
Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>