xfree86: Link fb statically

There's no real benefit to leaving this loadable, virtually every driver
is going to load it.

Reviewed-by: Jon Turney <jon.turney@dronecode.org.uk>
3 jobs for dash-z-now in 6 minutes and 25 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Docker Image
passed #442034
debian-testing

00:00:29

 
  Build And Test
passed #442035
autotools-build-and-test

00:05:55

passed #442036
meson-build-and-test

00:02:12