drm/i915: Combine cleanup_status_page()

Pull the physical status page cleanup into a common
cleanup_status_page() for caller simplicity.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180903152304.31589-1-chris@chris-wilson.co.uk