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>

Documentation/devicetree/bindings/pci/layerscape-pci.txt

@@ -34,7 +34,7 @@ Required properties:
   "intr": The interrupt that is asserted for controller interrupts
 - fsl,pcie-scfg: Must include two entries.
   The first entry must be a link to the SCFG device node
-  The second entry must be '0' or '1' based on physical PCIe controller index.
+  The second entry is the physical PCIe controller index starting from '0'.
   This is used to get SCFG PEXN registers
 - dma-coherent: Indicates that the hardware IP block can ensure the coherency
   of the data transferred from/to the IP block. This can avoid the software