INT 1A - Intel PCI BIOS v2.0c - WRITE CONFIGURATION BYTE (32-bit)
        AX = B18Bh
        BL = bus number
        BH = 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
SeeAlso: AX=B10Bh

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