drm/doc: Spinx leftovers

This is unfortunately not all the sphinx noise when building the gpu
documentations. But the remaining warnings have completely bogus line
and probably also file sources, and I just can't find them.

Probably some serious debuggging of the line annotations in the
sphinx/kernel-doc toolchain needed first.

Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1468612088-9721-11-git-send-email-daniel.vetter@ffwll.ch