Function 6504h          Get Filename Uppercase Table                 DOS 3.3+

    Returns the address of the filename uppercase table for the
    specified code page and country code. The table maps extended
    ASCII characters (ASCII value > 128) in filenames to their
    uppercase equivalents.

        Entry   AX    = 6504h
                BX    = Code page ID (0FFFFh = current code page)
                CX    = Size of buffer (min. 5)
                DX    = Country code (0FFFFh = current country)
                ES:DI = Pointer to country info buffer

        Return  Buffer updated
                or
                AX = Error code, if CF is set
                     | 01h Invalid function (CX < 5)
                     | 02h File not found

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    Format of country info buffer:
        Offset  Size    Description
        00h     1       Info-ID (= 04h)
        01h     4       32-bit address of filename uppercase table

    The filename uppercase table starts with a 16-bit value that
    specifies the length of the table; the remainder of the table
    specifies the uppercase equivalents of the ASCII characters from
    80h to 0FFh.