Initial Breakpoint support:

Initial Breakpoint support:

        * sim-main.h: (struct _sim_cpu): add cur_device field.
          Define cur_device values, breakpoint value, and SIM_ENGINE_HALT_HOOK
        * interp.c (sim_open): initialize cur_device
        * sky-engine.c (engine_run): use cur_device to set current_cpu
        * sky-libvpe.c (vpecallms_cycle): add check for breakpoint
        * sky-hardware.h: delete NUMBER_CPUS
        * sky-hardware.c (attach_devices): create a memory mapped comm
          area for GDB/SIM interactions

misc:
        * sky-vu.c ({read,write}_vu_misc_reg): do default behavior for
          unknown regs instead of sim_io_error. MP reg is float (was missing
          cast).