arm64: dts: imx8qxp: update pmu compatible

i.MX8QXP features four Cortex-A35 cores, use more accurate
compatible.
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8qxp.dtsi

@@ -141,7 +141,7 @@ dsp_reserved: dsp@92400000 {
 	};
 
 	pmu {
-		compatible = "arm,armv8-pmuv3";
+		compatible = "arm,cortex-a35-pmu";
 		interrupts = <GIC_PPI 7 IRQ_TYPE_LEVEL_HIGH>;
 	};