ARM: dts: doc: Document missing binding for omap5-mpu

The binding and support for omap5-mpu which has a cortex-a15
smp core, gic and integrated L2 cache has been existing for sometime.
So Documenting the missing binding here.

Cc: Benoit Cousson <bcousson@baylibre.com>
Signed-off-by: NSricharan R <r.sricharan@ti.com>
Signed-off-by: NRob Herring <rob.herring@calxeda.com>

Documentation/devicetree/bindings/arm/omap/mpu.txt

@@ -7,10 +7,18 @@ The MPU contain CPUs, GIC, L2 cache and a local PRCM.
 Required properties:
 - compatible : Should be "ti,omap3-mpu" for OMAP3
                Should be "ti,omap4-mpu" for OMAP4
+	       Should be "ti,omap5-mpu" for OMAP5
 - ti,hwmods: "mpu"
 
 Examples:
 
+- For an OMAP5 SMP system:
+
+mpu {
+    compatible = "ti,omap5-mpu";
+    ti,hwmods = "mpu"
+};
+
 - For an OMAP4 SMP system:
 
 mpu {