PCI: layerscape: Add LS1028a support

Add support for the LS1028a PCIe controller.

Signed-off-by: Xiaowei Bao <xiaowei.bao@nxp.com>
Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Andrew Murray <Andrew.Murray@arm.com>
Acked-by: Minghuan Lian <minghuan.Lian@nxp.com>