meson.build: KMS support also depends on dri2

Kernel modesettings support also depends on dri2, see
./hw/xfree86/drivers/modesetting/meson.build

So update meson.build to reflect the changes made in configure.ac by
commit 9c81b8f5

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
(cherry picked from commit 5d73a8b5)
3 jobs for backports-1.20 in 8 minutes and 39 seconds (queued for 1 second)
Status Name Job ID Coverage
  Docker Image
passed debian-testing #6201380

00:00:24

 
  Build And Test
passed autotools-build-and-test #6201381

00:08:14

passed meson-build-and-test #6201382

00:03:50