hmp: Restrict ILB events if no CPU has > 1 task

hmp: Restrict ILB events if no CPU has > 1 task

Frequently in HMP, the big CPUs are only active with one task per
CPU and there may be idle CPUs in the big cluster. This patch avoids
triggering an idle balance in situations where none of the active
CPUs in the current HMP domain have > 1 tasks running.

When packing is enabled, only enforce this behaviour when we are
not in the smallest domain - there we idle balance whenever a CPU
is over the up_threshold regardless of tasks in case one needs to
be moved.

Signed-off-by: Chris Redpath <chris.redpath@arm.com>
Signed-off-by: Jon Medhurst <tixy@linaro.org>