Set delays (Jr,AT model 339,XT286,PS)

        Entry:
          AH = 03h
          AL = subfunction
            0 reset typematic (PCjr)
            1 increase initial delay (PCjr)
            2 increase continuing delay (PCjr)
            3 increase both delays (PCjr)
            4 turn off typematic (PCjr)
            5 Set typematic rate (AT or PS/2)
          BH = 00 - 03 for delays of 250ms, 500ms, 750ms, or 1s
          BL = 00 - 1F for typematic rates of 30cps down to 2cps