INT 15 - Tandon memory mapper - Tandon MAPPER HARDWARE INITIALISATION CHECK ???
        AX = F200h
        CX = 454Dh
Return: CF clear if hardware already initialised
            BX = upper RAM areas in use
                bit 0: C000-C3FF
                bit 1: C400-C7FF
                ...
                bit 11: EC00-EFFF
        CF set if hardware not initialised yet