ARM: dts: imx51: Add M4IF support

As per the i.MX51 Reference Manual the M4IF register region
starts at 0x83fd8000 and has a 4kB address range.

Add support for it.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Tested-by: Sergey Lapin <sergey.lapin@cogentembedded.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx51.dtsi

@@ -531,6 +531,11 @@ audmux: audmux@83fd0000 {
 				status = "disabled";
 			};
 
+			m4if: m4if@83fd8000 {
+				compatible = "fsl,imx51-m4if";
+				reg = <0x83fd8000 0x1000>;
+			};
+
 			weim: weim@83fda000 {
 				#address-cells = <2>;
 				#size-cells = <1>;