-d tasks only tracks cpu0

[reticulatedpines]

Old code assumes only one cpu, eos_tasks_log_exec() logs task switches via eos_state->model->current_task_addr, which is only for cpu0.

Really this current_task_addr should be part of the cpu, not the model, or we need multiple current_task_addr fields for the model.

print_task_switch() should output which cpu it's logging (adding this but never seeing cpu1 is how I found this bug).

eos_tasks_log_exec() should be moved to the instruction monitoring plugin, qemu 4 doesn't provide accurate per instruction logging anymore so we may be missing events - and the plugin is faster. In practice task switch logging seems to work okay, maybe because large jumps tend to generate new TBs.