INT 4B - Virtual DMA Specification - RELEASE DMA BUFFFER
        AX = 8108h
        DX = flags
            bit 0: reserved (zero)
                1: data should be copied out of buffer
             2-15: reserved (zero)
        ES:DI -> DMA descriptor structure (see AX=8102h) with buffer ID set
                (also region size/region offset/segment if DX bit 1 set)
Return: CF clear if successful
        CF set on error
            AL = error code (see AX=8102h)