modesetting: Allow users to opt-in VRR support

Fetch VariableRefresh option value from X conf file for
modesetting backend DDX driver. This option defaults to false,
and must be set to "true" in conf file for variable refresh
support in the DDX driver.

Signed-off-by: Uday Kiran Pichika <pichika.uday.kiran@intel.com>
4 jobs for window_wrappers in 4 minutes and 57 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Docker Image
passed debian-testing #4445634

00:00:18

 
  Build And Test
passed autotools #4445635

00:04:38

passed meson #4445636

00:01:28

passed meson-noglamor #4445637

00:01:15