drm/i915: remove unused dev_priv->render_reclock_avail

Set from VBT, but never used. Good riddance.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1458834623-8734-5-git-send-email-jani.nikula@intel.com