drm/i915: add sprite restore function v3

To be used to restore sprite state on resume.

v2: move sprite tracking bits up so we don't track modified sprite state
v3: use src_x/y in sprite suspend/resume code (Ville)

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>