sched/fair: Add irq load awareness to the tick CPU selection logic

IRQ load is not taken into account when determining whether a task
should be migrated to a different CPU.  A task that runs for a long time
could get stuck on CPU with high IRQ load causing degraded performance.

Add irq load awareness to the tick CPU selection logic.

CRs-fixed: 809119
Change-Id: I7969f7dd947fb5d66fce0bedbc212bfb2d42c8c1
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>