HMP: Do not fork-boost tasks coming from PIDs <= 2

System services are generally started by init, whilst kernel threads
are started by kthreadd. We do not want to give those tasks a head
start, as this costs power for very little benefit. We do however
wish to do that for tasks which the user launches.

Further, some tasks allocate per-cpu timers directly after launch
which can lead to those tasks being always scheduled on a big CPU
when there is no computational need to do so. Not promoting services
to big CPUs on launch will prevent that unless a service allocates
their per-cpu resources after a period of intense computation, which
is not a common pattern.

Signed-off-by: Chris Redpath <chris.redpath@arm.com>
Signed-off-by: Jon Medhurst <tixy@linaro.org>
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>
Merge branch 'for-lsk' of git://git.linaro.org/arm/big.LITTLE/mp into lsk-v3.10-big.LITTLE