irqchip/renesas-irqc: Add r8a7795 INTC-EX DT documentation

For some reason the name of the external interrupt controller
has changed name with r8a7795, so use "intc-ex" instead of "irqc"
as r8a7795 compat string to follow the friendly documentation.
Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Reviewed-by: horms@verge.net.au
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: jason@lakedaemon.net
Cc: Magnus Damm <magnus.damm@gmail.com>
Link: http://lkml.kernel.org/r/20150928094228.32552.83336.sendpatchset@little-appleSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

Documentation/devicetree/bindings/interrupt-controller/renesas,irqc.txt

@@ -10,6 +10,7 @@ Required properties:
     - "renesas,irqc-r8a7792" (R-Car V2H)
     - "renesas,irqc-r8a7793" (R-Car M2-N)
     - "renesas,irqc-r8a7794" (R-Car E2)
+    - "renesas,intc-ex-r8a7795" (R-Car H3)
 - #interrupt-cells: has to be <2>: an interrupt index and flags, as defined in
   interrupts.txt in this directory
 - clocks: Must contain a reference to the functional clock.