ARM: dts: imx7: add CPU PMU support

Enable support for ARM Performance Monitoring Units available
on the Cortex-A7 CPU. There is only a single interrupt for the
PMU in both variants of the family, i.MX 7Solo and 7Dual.

Tested with perf on a i.MX 7Dual:
  hw perfevents: enabled with armv7_cortex_a7 PMU driver, 5 counters available
Signed-off-by: NStefan Agner <stefan@agner.ch>
Reviewed-by: NFabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx7s.dtsi

@@ -130,6 +130,12 @@
 		#phy-cells = <0>;
 	};
 
+	pmu {
+		compatible = "arm,cortex-a7-pmu";
+		interrupt-parent = <&gpc>;
+		interrupts = <GIC_SPI 92 IRQ_TYPE_LEVEL_HIGH>;
+		interrupt-affinity = <&cpu0>;
+	};
 
 	replicator {
 		/*