Add PCIe Endpoint mode compatible string "fsl,lx2160ar2-pcie-ep"

Link: https://lore.kernel.org/r/20201026051448.1913-1-Zhiqiang.Hou@nxp.com


Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rob Herring <robh@kernel.org>