INT 15 - Advanced Power Management Specification - CPU BUSY
        AX = 5306h
Return: CF clear
Notes:  called to ensure that the system runs at full speed even on systems
          where the BIOS is unable to recognize increased activity (especially
          if interrupts are hooked by other programs and not chained to the
          BIOS)
        this call may be made even when the system is already running at full
          speed, but it will create unnecessary overhead
        should not be called from within a hardware interrupt handler to avoid
          reentrance problems