dt-bindings: pci: layerscape-pci: Add EP mode compatible strings for ls1028a

Add EP mode compatible string for ls1028a.

Link: https://lore.kernel.org/r/20220311234938.8706-4-leoyang.li@nxp.com


Signed-off-by: Xiaowei Bao <xiaowei.bao@nxp.com>
Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Rob Herring <robh@kernel.org>