Scope Trace: Make it easier to trace through synchronous tasks

Tracing through synchronous tasks was a little troublesome because
the new thread's stack counter reset to 0.  This change allows
a synchronous task to set its trace level to be the same as the
thread that pushed the task.  For now, the task's level has to be
passed in the task's data structure but a future enhancement to the
taskprocessor subsystem could automatically set the trace level
of the servant to be that of the caller.

This doesn't really make sense for async tasks because you never
know when they're going to run anyway.

Change-Id: Ib8049c0b815063a45d8c7b0cb4e30b7b87b1d825