INT 21 - Phar Lap 386/DOS-Extender v3.0+ - READ/WRITE SYSTEM REGISTERS

	AX = 2535h
	EBX = direction (00h read registers, 01h write)
	DS:EDX -> system register record (see #01375)
Return: CF clear
Note:	this call is only available under MS Windows if PHARLAP.386 VDD is
	  installed