INT 21 - Phar Lap 386/DOS-Ext VMM v3.0+ - MIN/MAX EXTENDED/CONV MEMORY USAGE

	AX = 2536h
	EBX = bit flags
	    bit 0: modifying conventional memory rather than extended memory
	    bit 1: setting maximum memory usage rather than minimum
	ECX = new limit in 4K pages
Return: CF clear if successful
	    EAX = new limit
	CF set on error
	    EAX = error code (08h memory error or -NOPAGE set)
	    EBX = maximum limit in pages
	    ECX = minimum limit in pages