drm/i915: Move the pipe CRC stuff to other pipe data

Adding stuff to the bottom of struct drm_i915_driver_private is
nowadays considered uncool.

Cc: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>