arm64: dts: imx8mp: Add missing speed grade phandle

And missing speed grade phandle to cpu@0 node.
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Anson Huang <Anson.Huang@nxp.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: NXP Linux Team <linux-imx@nxp.com>
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mp.dtsi

@@ -59,6 +59,8 @@ A53_0: cpu@0 {
 			d-cache-line-size = <64>;
 			d-cache-sets = <128>;
 			next-level-cache = <&A53_L2>;
+			nvmem-cells = <&cpu_speed_grade>;
+			nvmem-cell-names = "speed_grade";
 			#cooling-cells = <2>;
 		};