INT 21 - DOS 3.2+ - IOCTL - SET LOGICAL DRIVE MAP
        AX = 440Fh
        BL = physical drive number (00h=default,01h=A:,etc))
Return: CF set on error
            AX = error code (01h,0Fh) (see AH=59h)
        CF clear if successful
            drive now responds to next logical drive number
Note:   maps logical drives to physical drives, similar to DOS's treatment of
          a single physical floppy drive as both A: and B:
SeeAlso: INT 2F/AX=122Bh