Perf: arm64: stop counters when going into hotplug

Hotplug disables the pmu irq, but if counters are
running in the window before the CPU is hotplugged off
they can overflow and generate an interrupt. Because the
interrupt is disabled, this prevents the cpu from going
down.

Events are stopped during hotplug processing. However,
perf is hooked into the timer tick, and restarts enabled
events on every tick, even if they were stopped. Change
the event state to OFF to prevent this.

CPUs can still be power-collapsed while being hotplugged
off, but hotplug processing will save and restore the correct
state, so don't process power-collapse save/restore while
hotplug is in process.

Processing for stop reads the counters, so a separate call
is no longer needed. Start processing re-enables events so
the from_idle flag is not needed during pmu_enable.

Change-Id: I6a7f5b04955ebba8c4d76547f24e2be4071d7539
Signed-off-by: Neil Leeder <nleeder@codeaurora.org>