Int 1A Fn B18B  - Pci Bios V2.0c+ - Write Configuration Byte (32-bit)      [X]

   AX = B18Bh
   BH = bus number
   BL = device/function number (bits 7-3 device, bits 2-0 function)
   DI = register number (0000h-00FFh)
   CL = byte to write

Return: as for AX=B10Bh

Note:  the meanings of BL and BH on return were exchanged between the initial
     drafts of the specification and final implementation

See Also: AX=B10Bh,AX=B18Ch,AX=B18Dh