sched: Optimize scheduler trace events to reduce trace buffer usage

Scheduler ftrace events currently generate a lot of data when turned
on. The excessive log messages often end up overflowing trace buffers
for long use cases or crowding out other events. Optimize scheduler
events so that the log spew is less and more manageable. To that end
change the variable type for some event fields; introduce variants
of sched_cpu_load that can be turned on/off for separate code paths
and remove unused fields from various events.

Change-Id: I2b313542b39ad5e09a01ad1303b5dfe2c4883b8a
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>