dt-bindings: pci: layerscape-pci: add compatible strings "fsl, ls1028a-pcie"

Add the PCIe compatible string for LS1028A.
Signed-off-by: NXiaowei Bao <xiaowei.bao@nxp.com>
Signed-off-by: NHou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Reviewed-by: NAndrew Murray <andrew.murray@arm.com>

Documentation/devicetree/bindings/pci/layerscape-pci.txt

@@ -21,6 +21,7 @@ Required properties:
         "fsl,ls1046a-pcie"
         "fsl,ls1043a-pcie"
         "fsl,ls1012a-pcie"
+        "fsl,ls1028a-pcie"
   EP mode:
 	"fsl,ls1046a-pcie-ep", "fsl,ls-pcie-ep"
 - reg: base addresses and lengths of the PCIe controller register blocks.