DC_Sp, handle Director/CLI settings

RST 20H, DEFW $180C

IN:

     C = reason code
     B = 0, always
     HL = points to a null-terminated string, the argument

     $00 DQ_Dev : define default device 
     $03 DQ_Dir : define default directory 
     $06 DQ_Fnm : define filename match string

OUT:

     Fc = 0:   Successful
     Fc = 1:   Failure, A = RC error

Internal operating system usage.
This call is used by the OS_NQ if B = $8C.
Use it directly for these reasons (instead of OS_SP). It will be faster.