Take a first pass at capturing the need for light weight interrupt
thread and kernel thread context switch optimization. Point at
Bosko as having done some useful work here, but don't assign an
owner. I suspect we'll need to refine the wording here, assign
owners for platforms, and break this into a couple of items -- perhaps
breaking out the interrupt issue vs. the general context switch
issue. Feedback welcomed.

This is a 5.2-RELEASE "must have" since this work will be required
to further restore performance from RELENG_4.