Add functions to System object to set up function-based events,

Add functions to System object to set up function-based events,
including automatically fixing up addresses to deal with
optionally executed Alpha gp update prolog.

SConscript:
    Remove freebsd_events.cc and linux_events.cc.
base/remote_gdb.cc:
cpu/pc_event.cc:
kern/system_events.cc:
kern/system_events.hh:
    PCEvents now schedule themselves in constructor.
cpu/pc_event.hh:
    PCEvents now schedule themselves in the constructor.
    Get rid of constructor versions that don't take an address and
    all the schedule() methods that are now unnecessary.
kern/freebsd/freebsd_system.cc:
kern/freebsd/freebsd_system.hh:
    Use new System methods to schedule function-based events.
    Move FreeBSD-specific function event classes into FreebsdSystem.
kern/linux/linux_system.cc:
kern/linux/linux_system.hh:
    Use new System methods to schedule function-based events.
    Move Linux-specific function event classes into LinuxSystem.
kern/tru64/tru64_events.hh:
    PCEvents now schedule themselves in constructor.
    Add DebugPrintfrEvent to encapsulate raw setting as new type
    (to work better with new System function-event method.)
kern/tru64/tru64_system.cc:
    Use new System methods to schedule function-based events.
kern/tru64/tru64_system.hh:
    Add DebugPrintfrEvent to encapsulate raw setting as new type
    (to work better with new System function-event method.)
sim/system.cc:
sim/system.hh:
    Add functions to set up function-based events, including
    automatically fixing up addresses to deal with optionally
    executed Alpha gp update prolog.

--HG--
extra : convert_revision : c2cf09144297b6602afe755a34a0a2227023783f