INT 10 - Diamond Stealth 24 - SET/RESET DUAL DISPLAY MODE

	AX = 4FFFh
	BX = dual display mode
	    00h reset
	    01h set dual display, 32KB VGA test
	    02h set dual display, 64KB VGA test
Return: AX = 4F00h if successful
	    BX = number of scanlines off screen for test mode