arm64: dts: rockchip: support the pmu node for rk3399

This patch adds to enable the ARM Performance Monitor Units for rk3399.
ARM cores often have a PMU for counting cpu and cache events like cache
misses and hits.

This uses the new interrupt-partition mechanism to allow the two pmu
instances to use the per-cpu interrupt.

Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>