tracing: add previous task state info to sched switch event

It is useful to see the state of a task that is being switched out.
This patch adds the output of the state of the previous task in
the context switch event.

[ Impact: see state of switched out task in context switch ]

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>