arm64: dts: r8a7795: pmu: switch to Cortex specific device nodes

Instead of using the generic armv8-pmuv3 compatibility use the more
specific Cortex A57 compatibility.
Signed-off-by: Dirk Behme <dirk.behme@gmail.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm64/boot/dts/renesas/r8a7795.dtsi

@@ -246,8 +246,8 @@ gpio7: gpio@e6055800 {
 			power-domains = <&cpg>;
 		};
 
-		pmu {
-			compatible = "arm,armv8-pmuv3";
+		pmu_a57 {
+			compatible = "arm,cortex-a57-pmu";
 			interrupts = <GIC_SPI 72 IRQ_TYPE_LEVEL_HIGH>,
 				     <GIC_SPI 73 IRQ_TYPE_LEVEL_HIGH>,
 				     <GIC_SPI 74 IRQ_TYPE_LEVEL_HIGH>,