drm/i915: move dev_priv->(rps|ips) out of line

And give the structs slightly more generic names. I've decided to keep
the short rps/ips prefix, since that's just easier and less churn.

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>