dt-bindings: irq: imx-irqsteer: Add multi output interrupts support

One irqsteer channel can support up to 8 output interrupts.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: devicetree@vger.kernel.org
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

Documentation/devicetree/bindings/interrupt-controller/fsl,irqsteer.txt

@@ -6,8 +6,9 @@ Required properties:
 	- "fsl,imx8m-irqsteer"
 	- "fsl,imx-irqsteer"
 - reg: Physical base address and size of registers.
-- interrupts: Should contain the parent interrupt line used to multiplex the
-  input interrupts.
+- interrupts: Should contain the up to 8 parent interrupt lines used to
+  multiplex the input interrupts. They should be specified sequentially
+  from output 0 to 7.
 - clocks: Should contain one clock for entry in clock-names
   see Documentation/devicetree/bindings/clock/clock-bindings.txt
 - clock-names: