xorg force VGA output only

or say, disable/ignore LVDS output, referred from X Quirks - Ubuntu wiki:

1. use the command to generate an xorg.conf (from Xorg - ArchWiki): Xorg -configure mv /root/xorg.conf.new /etc/X11/xorg.conf
2. In section "Section "Device"" of xorg.conf add the line: Option "monitor-LVDS" "LVDS"
3. Then the following new section: Section "Monitor" Identifier "LVDS" Option "Ignore" "True" EndSection

Why should I do this? Well, when you mess up your display panel of your laptop and get a radeon driver which binds LVDS and VGA together...