INT 4B - Virtual DMA Specification - REQUEST DMA BUFFER

	AX = 8107h
	DX = flags
	    bit 0: reserved (zero)
	    bit 1: data should be copied into buffer
	    bits  2-15 reserved (zero)
	ES:DI -> DMA descriptor structure (see #03221) with region size set
		  (also region offset and region segment if DX bit 1 set)
Return: CF clear if successful
	    DDS physical address and buffer ID set
	    DDS region size filled with length of buffer
	CF set on error
	    AL = error code (see #03218)
SeeAlso: AX=8108h