ARM: dts: r8a7793: add m2 clock to device tree

Declare m2 clock in r8a7793 device tree.

Based on similar work for the r8a7791 by Laurent Pinchart.
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7793.dtsi

@@ -817,6 +817,14 @@ p_clk: p_clk {
 			clock-mult = <1>;
 			clock-output-names = "p";
 		};
+		m2_clk: m2_clk {
+			compatible = "fixed-factor-clock";
+			clocks = <&cpg_clocks R8A7793_CLK_PLL1>;
+			#clock-cells = <0>;
+			clock-div = <8>;
+			clock-mult = <1>;
+			clock-output-names = "m2";
+		};
 		rclk_clk: rclk_clk {
 			compatible = "fixed-factor-clock";
 			clocks = <&cpg_clocks R8A7793_CLK_PLL1>;