INT 15 - EISA SYSTEM ROM - WRITE NONVOLATILE MEMORY
        AX = D803h
        CX = length of data structure (0000h = empty slot)
                includes two bytes for config file checksum
        DS:SI -> configuration data
Return: CF clear if successful
            AH = 00h
        CF set on error
            AH = error code
                84h error clearing CMOS
                85h EISA CMOS is full
                86h invalid BIOS-FW function call
Note:   call with AL=83h if using 32-bit CS addressing mode instead of 16-bit
SeeAlso: AX=D802h

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