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 24 seconds (queued for 1 second)
Status Job ID Name Coverage
  Container Prep
passed #387782
container_prep

00:00:20

 
  Build
failed #387783
build-native-meson

00:01:04

 
Name Stage Failure
failed
build-native-meson Build
  RemovedInSphinx30Warning)
/root/.local/lib/python3.5/site-packages/sphinx_rtd_theme/search.html:20: RemovedInSphinx30Warning: To modify script_files in the theme is deprecated. Please insert a <script> tag directly in your theme instead.
{{ super() }}
ninja: build stopped: cannot make progress due to previous errors.
Uploading artifacts...
build-*/meson-logs: found 2 matching files
prefix-*: found 54 matching files

Uploading artifacts to coordinator... ok
id=387783 responseStatus=201 Created token=66JZK51L
ERROR: Job failed: exit code 1