dmabuf: Create buffers without the SCANOUT flag

gbm_bo_create_with_modifiers implies the GBM_BO_USE_SCANOUT flag, which
disables complex (tiled or compressed) formats that cannot be used for
scanout. This reduces performance. We don't need to scan out buffers
created for sceencasting/etc., so this is suboptimal.

By switching to gbm_bo_create_with_modifiers2, we can explicitly pass
the flags and avoid falling back to lower performance formats. Also add
a config check and fall back to the old version, to retain compatibility
with older mesa versions.