perf: Add support for exclude_idle attribute

Enable the perf exclude_idle event attribute to avoid waking
possilby sleeping CPUS. The counter values are updated when CPU
enters idle. If the CPU is idle when perf reads the current
event value (of an exclude idle event) then the value from
when the CPU went idle is returned.
This commit supercedes the commits below. The context for the
commits below changed too much to enable cherry-picking.
commit 573979dee2a7 ("perf: Add support for exclude_idle attribute")
commit 54f6e4ae87be ("perf: Enable updating exclude_idle events
at idle")
commit 960dbb1751f3 ("perf: Skip permission checks on kernel owned
perf events")

Squashed commit:
Perf: arm64: enable idle_update at end of probe

Currently armv8pmu_idle_update is enabled before
arm_pmu_device_probe has completed. arm_pmu_device_probe
initializes some structures need by armv8pmu_idle_update.
armv8pmu_idle_update can get called before these structures
are complete leading to seg faults. Set a flag to prevent
armv8pmu_idle_update from trying to access these structures
until arm_pmu_device_probe is finished. Also move the call
to perf_event_cpu_hp_init after arm_pmu_device_probe so
that hotplug doesn't overwrite the flag.

Change-Id: Ib554c9fe106963ec1b42e72aeaf84fc73201bbb7
Signed-off-by: Patrick Fay <pfay@codeaurora.org>
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>