arm64: dts: layerscape: Add PCIe EP node for ls1088a

Add PCIe EP node for ls1088a to support EP mode.

Signed-off-by: Xiaowei Bao <xiaowei.bao@nxp.com>
Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>