PCI: layerscape: Add EP mode support for ls1088a and ls2088a

Add PCIe EP mode support for ls1088a and ls2088a, there are some
difference between LS1 and LS2 platform, so refactor the code of
the EP driver.

Link: https://lore.kernel.org/r/20200918080024.13639-10-Zhiqiang.Hou@nxp.com


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: Rob Herring <robh@kernel.org>