arm64: dts: imx93: add MU clock for mailbox

Add MU clock for mailbox usage
Reviewed-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx93.dtsi

@@ -135,6 +135,7 @@ mu1: mailbox@44230000 {
 				compatible = "fsl,imx93-mu", "fsl,imx8ulp-mu";
 				reg = <0x44230000 0x10000>;
 				interrupts = <GIC_SPI 22 IRQ_TYPE_LEVEL_HIGH>;
+				clocks = <&clk IMX93_CLK_MU1_B_GATE>;
 				#mbox-cells = <2>;
 				status = "disabled";
 			};
@@ -271,6 +272,7 @@ mu2: mailbox@42440000 {
 				compatible = "fsl,imx93-mu", "fsl,imx8ulp-mu";
 				reg = <0x42440000 0x10000>;
 				interrupts = <GIC_SPI 24 IRQ_TYPE_LEVEL_HIGH>;
+				clocks = <&clk IMX93_CLK_MU2_B_GATE>;
 				#mbox-cells = <2>;
 				status = "disabled";
 			};