INT 2F U - Quarterdeck - GET QD HIMEM PRESENCE
        AX = D201h
        BX = 4849h ("HI")
        CX = 4D45h ("ME")
        DX = 4D51h ("MQ")
Return: BX = 4F4Bh ("OK")
        ES:DI -> HIMEM entry point
Notes:  QEMM/QRAM/VIDRAM/MANIFEST will search for a free AH value from D2h
          through FFh, then C0h through D1h