INT 15 - later PSIBM PS/2, any model/2s - READ BOOT DEVICE ID
	AX = D600h
	BL = 00h
	DX = device ID
Return: CF clear if successful
	    AH = 00h
	CF set on error
	    AH = status (86h for function not supported)
SeeAlso: AX=D600h/BL=01h,AX=D601h/BL=00h,AX=D602h