[PATCH] drivers: perf: arm: implement CPU_PM notifier

Lorenzo Pieralisi [off-list ref] writes:

When a CPU is suspended (either through suspend-to-RAM or CPUidle),
its PMU registers content can be lost, which means that counters
registers values that were initialized on power down entry have to be
reprogrammed on power-up to make sure the counters set-up is preserved

This assumes that the PMUs are always sharing a power rail with a
specific CPU, not the cluster.  Is that a reliable assumption?

Kevin