pci: layerscape: Add size check for config resource

resource "config" is required to have minimum 8KB space
as per hardware documentation.

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