Stephen Morris:
To get F21 to recognize your monitor you could put a file with the same monitor device sections that you normally put in xorg.conf into /etc/X11/xorg.conf.d. That directory is where xorg reads it configuration files from these days.
Beartooth:
That file does exist (to my surprise; dunno how I missed it). But it contains only a config file for the keyboard. There isn't any for the monitor at all.
As I understand it, you fill that directory with whatever configuration files you want, and it'll go through all of them. Rather than have one xorg.conf file that did everything, you now have a file for your keyboard (if needed), another file for your screen (if needed), etc.
So, whatever you used to put into xorg.conf to customise your computer, now put it into a file in that directory.