Documentation: dt: OMAP: l3-noc: Add *reg* in required properties

OMAP L3 driver needs reg address space for its operation
and hence its a required property.
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>

Documentation/devicetree/bindings/arm/omap/l3-noc.txt

@@ -6,6 +6,7 @@ provided by Arteris.
 Required properties:
 - compatible : Should be "ti,omap3-l3-smx" for OMAP3 family
                Should be "ti,omap4-l3-noc" for OMAP4 family
+- reg:	Contains L3 register address range for each noc domain.
 - ti,hwmods: "l3_main_1", ... One hwmod for each noc domain.
 
 Examples: