tracing/sched: add load balancer tracepoint

When doing performance analysis it can be useful to see exactly
what is going on with the load balancer - when it runs and why
exactly it may not be redistributing load.

This additional tracepoint will show the idle context of the
load balance operation (idle, not idle, newly idle), various
values from the load balancing operation, the final result,
and the new balance interval.

Change-Id: I1538c411c5f9d17d7d37d84ead6210756be2d884
Signed-off-by: Steve Muckle <smuckle@codeaurora.org>