irqchip: renesas-intc-irqpin: Document SoC-specific bindings

The documentation only mentioned the generic fallback compatible property.
Add the missing SoC-specific compatible properties, which are already in
use.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Link: https://lkml.kernel.org/r/1409212800-4957-1-git-send-email-geert+renesas@glider.be
Signed-off-by: Jason Cooper <jason@lakedaemon.net>

Documentation/devicetree/bindings/interrupt-controller/renesas,intc-irqpin.txt

@@ -2,7 +2,13 @@ DT bindings for the R-/SH-Mobile irqpin controller
 
 Required properties:
 
-- compatible: has to be "renesas,intc-irqpin"
+- compatible: has to be "renesas,intc-irqpin-<soctype>", "renesas,intc-irqpin"
+  as fallback.
+  Examples with soctypes are:
+    - "renesas,intc-irqpin-r8a7740" (R-Mobile A1)
+    - "renesas,intc-irqpin-r8a7778" (R-Car M1A)
+    - "renesas,intc-irqpin-r8a7779" (R-Car H1)
+    - "renesas,intc-irqpin-sh73a0" (SH-Mobile AG5)
 - #interrupt-cells: has to be <2>: an interrupt index and flags, as defined in
   interrupts.txt in this directory