With the appearance of the this new Option the X Server would crash if the
option is not set.
Default dmabuf_capable to off/FALSE for now - a user without knowledge about
this option does not want to enable it until its save.
Fixes: d11d5bb80 ("glamor: Hide new DRI behind Option "Debug" "dmabuf_capable")
Signed-off-by: Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Reviewed-by: Adam Jackson <ajax@redhat.com>