dt-bindings: pci: layerscape-pci: Update the description of SCFG property

Update the description of the second entry of 'fsl,pcie-scfg' property,
as the LS1043A PCIe controller also has some control registers in SCFG
block, while it has 3 controllers.

Link: https://lore.kernel.org/r/20220311234938.8706-3-leoyang.li@nxp.com


Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Rob Herring <robh@kernel.org>