Allow CPUs to specify their own CPU ids.

Allow CPUs to specify their own CPU ids.
Make the AlphaConsole calculate the number of CPUs instead
of passing that in as a parameter.

cpu/base.cc:
    pass the desired cpu_id into registerExecContext, offsetting it
    by the thread number.  a cpu_id of -1 means that it should be
    generated for you.
cpu/base.hh:
    Take the cpu_id as a parameter
cpu/o3/alpha_cpu_builder.cc:
cpu/simple/cpu.cc:
    Accept the cpu_id as a parameter
    while we're here, let's remove the multiplier since it is
    not used.
dev/alpha_console.cc:
    don't take the number of CPUs as a parameter.  Calculate it from
    the system based on the number of CPUs that have been registered.
    move init() code to startup() to ensure that all CPUs are registerd.
dev/alpha_console.hh:
python/m5/objects/AlphaConsole.py:
    don't take the number of CPUs as a parameter.
    move init() code to startup() to ensure that all CPUs are registerd.
python/m5/objects/BaseCPU.py:
    take the cpu_id as a parameter.  Default it to -1 which means
    that it will be generated.
sim/system.cc:
    allow the registerExecContext functioin to take a desired
    cpu_id as a parameter.  Check to ensure that the id isn't
    already used.  Accept -1 as a request to have an id assigned.
sim/system.hh:
    keep track of the number of registered exec contexts.
    provide a function for accessing the number of exec contexts
    that checks to ensure that they are all registered correctly.

--HG--
extra : convert_revision : 8e12f96ff8a49fa16cdbbdb4c05c651376c35788