Get enhanced shift flags (AT model 339,XT2,XT286,PS)

        Entry:
          AH = 12h
        Return:
          AL = (same as for AH=02)
           1xxx xxxx  Ins ON
           x1xx xxxx  CapsLock ON
           xx1x xxxx  NumLock ON
           xxx1 xxxx  ScrollLock ON
           xxxx 1xxx  Either ALT key down
           xxxx x1xx  Either CTRL key down
           xxxx xx1x  Left shift key down
           xxxx xxx1  Right shift key down
          AH =
           1xxx xxxx  SysReq key down
           x1xx xxxx  CapsLock key down
           xx1x xxxx  NumLock key down
           xxx1 xxxx  ScrollLock key down
           xxxx 1xxx  Right Alt key down
           xxxx x1xx  Right Ctrl key down
           xxxx xx1x  Left Alt key down
           xxxx xxx1  Right Alt key down