hpst Modern Linux distributions don't require xorg.conf anymore since everything is done automatically. But you could always create a small xorg.conf yourself that includes no more than your desired option (plus required formatting).
I currently don't have access to my machines so I can't look it up at the moment.
This might be all you need in a newly created xorg.conf to use fbdev:
Identifier "Intel Graphics" #I believe this could be any string
You could also place such a small file in /etc/X11/Xorg.conf.d
It might depend on your Linux distribution.
This is how it would work for Arch Linux: https://wiki.archlinux.org/index.php/Intel_graphics#Xorg_configuration
Make sure you know how to switch to a terminal and edit files on the command line in case your graphical desktop won't start anymore after the change.
Xorg has a log file which tells you what driver it chose. It can be a pain to read through though. The location might depend on your distribution, too.