added system option to bin interrupt code seperately.

added system option to bin interrupt code seperately.

arch/alpha/ev5.cc:
    set the mode explictly rather than having a bool user/notuser
cpu/simple_cpu/simple_cpu.hh:
    there is no class Kernel
kern/kernel_stats.cc:
    use cpu_mode_num
kern/kernel_stats.hh:
    add interrupt mode and use cpu_mode_num rather than constant
kern/linux/linux_system.cc:
kern/linux/linux_system.hh:
kern/system_events.cc:
kern/system_events.hh:
    add events to change the mode to/from interrupt
sim/system.cc:
sim/system.hh:
    add a pal symbol table

--HG--
extra : convert_revision : 9d30e826b72122062a5ea12d094f94760e75c66a