backend-drm: use format db for fallback too

Replace one more open-coded pixel format translation map with a call to our
central pixel format database, reducing duplication of format information.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
2 jobs for mr/alpha-substitute in 1 minute and 20 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Container Prep
passed #683805
container_prep

00:00:25

 
  Build
passed #683806
build-native-meson

00:00:55