Compatibility: EMS 3.2+
Expects: AX    4200H
Returns: AH    EMM status (0=successful)
DX    total pages (16K units)
BX    available pages (16K units)
Info: Obtains the total amount of EMS memory that is supported and the
amount that is currently available.

Notes: DOS 6.0+ EMM386 draws EMS from the same pools as XMS ; so the
returned values may vary from time to time.

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INT 67H 4200H: Get EMS Memory Total / Available