Create one timeline context for each CRTC to be able to handle out-fences
and signal them. It adds a few members to struct drm_crtc: fence_context,
where we store the context we get from fence_context_alloc(), the
fence seqno and the fence lock, that we pass in fence_init() to be
used by the fence.

v2: Comment by Daniel Stone:
	- add BUG_ON() to fence_to_crtc() macro

v3: Comment by Ville Syrjälä
	- Use more meaningful name as crtc timeline name

v4: Comments by Brian Starkey
	- Use even more meaninful name for the crtc timeline
	- add doc for timeline_name
    Comment by Daniel Vetter
	- use in-line style for comments

    - rebase after fence -> dma_fence rename

v5: Comment by Daniel Vetter
	- Add doc for drm_crtc_fence_ops

v6: Comment by Chris Wilson
	- Move fence_to_crtc to drm_crtc.c
	- Move export of drm_crtc_fence_ops to drm_crtc_internal.h

    - rebase against latest drm-misc
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v5)
Reviewed-by: Sean Paul <seanpaul@chromium.org> (v5)
Tested-by: Robert Foss <robert.foss@collabora.com> (v5)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1479220628-10204-1-git-send-email-gustavo@padovan.org