drm/fence: add in-fences support

There is now a new property called IN_FENCE_FD attached to every plane
state that receives sync_file fds from userspace via the atomic commit
IOCTL.

The fd is then translated to a fence (that may be a fence_array
subclass or just a normal fence) and then used by DRM to fence_wait() for
all fences in the sync_file to signal. So it only commits when all
framebuffers are ready to scanout.

v2: Comments by Daniel Vetter:
	- remove set state->fence = NULL in destroy phase
	- accept fence -1 as valid and just return 0
	- do not call fence_get() - sync_file_fences_get() already calls it
	- fence_put() if state->fence is already set, in case userspace
	set the property more than once.

v3: WARN_ON if fence is set but state has no FB

v4: Comment from Maarten Lankhorst
	- allow set fence with no related fb

v5: rename FENCE_FD to IN_FENCE_FD

v6: Comments by Daniel Vetter:
	- rename plane_state->in_fence back to "fence"
	- re-introduce WARN_ON if fence set but no fb

     - rebase after fence -> dma_fence rename

v7: Comments by Brian Starkey
	- set state->fence to NULL when duplicating the state
	- fail if IN_FENCE_FD was already set

v8: rebase against latest drm-misc

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Brian Starkey <brian.starkey@arm.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Tested-by: Robert Foss <robert.foss@collabora.com>
[danvet: Rebase onto extracted drm_mode_config.[hc].]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index 5d11b25..c6754cc 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -481,6 +481,11 @@ struct drm_mode_config {
 	 */
 	struct drm_property *prop_fb_id;
 	/**
+	 * @prop_in_fence_fd: Sync File fd representing the incoming fences
+	 * for a Plane.
+	 */
+	struct drm_property *prop_in_fence_fd;
+	/**
 	 * @prop_crtc_id: Default atomic plane property to specify the
 	 * &drm_crtc.
 	 */