emulate callpal halt for non FULL_SYSTEM

emulate callpal halt for non FULL_SYSTEM
in the process make m5_exit more generic

arch/alpha/ev5.cc:
arch/alpha/ev5.hh:
    There's no reason that this needs to be in an arch specific file
arch/alpha/isa_desc:
    m5_exit -> SimExit
    Emulate callpal halt and cause the simulator to exit
    while we're at it, sort #includes
sim/sim_events.cc:
sim/sim_events.hh:
    move the m5_exit function here, renaming it to SimExit.
    Also Allow the caller to pass in the termination message.

--HG--
extra : convert_revision : 54b43b17a412ab387b8672c27ef0b04fce10ee15