Reset driver and read status

        Entry:
          AX = 0000h

        Return:
          AX = status
               0  hardware/driver not installed
               -1 hardware/driver installed
          BX = number of buttons
               -1 two buttons
               0  other than two
               3  Mouse Systems mouse

        Note:   to use mouse on a Hercules-compatible monographics card in
                graphics mode, you must first set 0040h:0049h to 6 for page
                0 or 5 for page 1, and then call this function.