dt-bindings: mrvl,intc: Add a MMP3 interrupt controller

Similar to MMP2 one, but has an extra range for the other core. The
muxes stay the same.
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Reviewed-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/interrupt-controller/mrvl,intc.txt

 * Marvell MMP Interrupt controller
 
 Required properties:
-- compatible : Should be "mrvl,mmp-intc", "mrvl,mmp2-intc" or
-  "mrvl,mmp2-mux-intc"
+- compatible : Should be
+               "mrvl,mmp-intc" on Marvel MMP,
+               "mrvl,mmp2-intc" along with "mrvl,mmp2-mux-intc" on MMP2 or
+               "marvell,mmp3-intc" with "mrvl,mmp2-mux-intc" on MMP3
 - reg : Address and length of the register set of the interrupt controller.
   If the interrupt controller is intc, address and length means the range
-  of the whole interrupt controller. If the interrupt controller is mux-intc,
-  address and length means one register. Since address of mux-intc is in the
-  range of intc. mux-intc is secondary interrupt controller.
+  of the whole interrupt controller. The "marvell,mmp3-intc" controller
+  also has a secondary range for the second CPU core.  If the interrupt
+  controller is mux-intc, address and length means one register. Since
+  address of mux-intc is in the range of intc. mux-intc is secondary
+  interrupt controller.
 - reg-names : Name of the register set of the interrupt controller. It's
   only required in mux-intc interrupt controller.
 - interrupts : Should be the port interrupt shared by mux interrupts. It's