backend-drm: make linear modifier to default

Make the linear modifier to the default of DRM format modifiers if
supported modifiers isn't get from kernel driver.
2 jobs for default-linear-modifiers in 1 minute and 44 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Container Prep
passed #386705
container_prep

00:00:17

 
  Build
passed #386706
build-native-meson

00:01:27