drm/i915: Rename fence.lru_list to link

Our current practice is to only name the actual list (here
dev_priv->fence_list) using "list", and elements upon that list are
referred to as "link". Further, the lru nature is of the list and not of
the node and including in the name does not disambiguate the link from
anything else.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160818161718.27187-20-chris@chris-wilson.co.uk