xfree86: Merge vbe into int10

There's not really a good reason to keep these separate, the vbe code
requires int10 and is not very large. This change eliminates the
build-time options for vbe; if you build int10, you get vbe.

Gitlab: xorg/xserver#692
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
3 jobs for dash-z-now in 7 minutes and 1 second (queued for 2 seconds)
Status Job ID Name Coverage
  Docker Image
passed #688187
debian-testing

00:00:36

 
  Build And Test
passed #688188
autotools-build-and-test

00:06:24

passed #688189
meson-build-and-test

00:02:36