4K on RPI4?

[James Gritton]

I'd like to move my desktop to FreeBSD for the first time in some years, 
and I have an 8GB RPI4 that's working nicely on CURRENT, except that 
Xorg insists that my resolution is 1920x1080.  I've got a nice 60Hz 4K 
monitor, so it's kind of a shame to only have a quarter of the pixels I 
should have.

How do I convince the X server (or the kernel, or whoever) that it's OK 
to give me some 4K output.  And if I can get that going, my next 
question will be about 60Hz (when I specify it according to the RPI 
instructions, the kernel doesn't fully boot).  But speed is icing on the 
cake - I just want those pixels!

- Jamie