pci: layerscape: Add specific config entry for RC and EP mode driver

Add Root Complex and Endpoint mode specific config entries, such that
it's feasible to enable the RC and/or EP mode driver indepently.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>