deprecate the m5exit instruction and rename it to m5exit_old

deprecate the m5exit instruction and rename it to m5exit_old
Implement a new m5exit instruction with an optional delay

arch/alpha/isa_desc:
    move m5exit to m5exit old.  The old version of the
    instruction is now deprecated

    Implement the new exit instruction with the optional delay
sim/sim_events.cc:
sim/sim_events.hh:
    Make SimExit take a cycle
sim/universe.cc:
    provide ticksPerMS, ticksPerUS, and ticksPerNS so we don't
    have to do math during the cycle

--HG--
extra : convert_revision : e2ed47a2e5cfcd57c82086c6fcb4a28bf801c214