powerpc: Update Integrated Flash controller device tree bindings

Freescale's Integrated Flash controller (IFC) may have one or two
interrupts. In case of single interrupt line, it will cover all IFC
interrupts.

Update this information in IFC device tree bindings

Signed-off-by: Prabhakar Kushwaha <[e-mail]>
Signed-off-by: Kumar Gala <[e-mail]>

Documentation/devicetree/bindings/powerpc/fsl/ifc.txt

···
 - #size-cells : Either one or two, depending on how large each chipselect
                 can be.
 - reg : Offset and length of the register set for the device
-- interrupts : IFC has two interrupts. The first one is the "common"
-               interrupt(CM_EVTER_STAT), and second is the NAND interrupt
-               (NAND_EVTER_STAT).
+- interrupts: IFC may have one or two interrupts.  If two interrupt
+              specifiers are present, the first is the "common"
+              interrupt (CM_EVTER_STAT), and the second is the NAND
+              interrupt (NAND_EVTER_STAT).  If there is only one,
+              that interrupt reports both types of event.
+
 
 - ranges : Each range corresponds to a single chipselect, and covers
            the entire access window as configured.