sched: walt: Add a tracepoint to record load update information

When updating the cpu frequency governor with load
information, it's useful to trace what's being
reported from the sched side as well. Add a trace
point that records the various stats. There is some
redundancy with other tracepoints, but the ones that
do have the relevant information are too frequent and
usually overrun trace buffers.

Change-Id: I6b5d30034cce942e0bc0083af8493dca77060564
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>