ARM64: dts: marvell: armada-37xx: Wire PMUv3

The Cortex-A53s that power the Armada-37xx SoCs are equipped with
a PMUv3, just like most ARMv8 cores.

Advertise the PMUv3 presence in the device tree, and wire its
interrupt. This allows the perf subsystem to work correctly.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>