Switch out fixes for CPUs.

Switch out fixes for CPUs.

src/cpu/o3/cpu.cc:
    Fix up keeping proper state when switched out and drained.
src/cpu/simple/timing.cc:
src/cpu/simple/timing.hh:
    Keep track of the event we use to schedule fetch initially and upon resume.  We may have to cancel the event if the CPU is switched out.

--HG--
extra : convert_revision : 60a2a1bd2cdc67bd53ca4a67aa77166c826a4c8c