Replace DRI2 backend by DRI3

Signed-off-by: Axel Davy <axel.davy@ens.fr>
Cleanups

Signed-off-by: Axel Davy <axel.davy@ens.fr>
Rename dri2 to dri3

Signed-off-by: Axel Davy <axel.davy@ens.fr>