- Ensure FIQs are enabled when cpu_idle() is called.
- Remove unused members of irq_cpustat_t.
- Remove unnecessary #ifndef CONFIG_SMP...#endif around irq_exit()
  macro.
- Rename __stf/__clf such that it stresses that they affect only
  local state (as per local_irq_xxx).
- Move THREAD_SIZE such that it can be used in current_thread_info()