drm: Use struct fb_info * as arg for syscons fb restore helper function.

drm: Use struct fb_info * as arg for syscons fb restore helper function.

* This makes the framebuffer api handling in drm slightly nicer, and
  reduces the diffs in drm/radeonkms/i915 a bit.

* Renames the cookie element in struct fb_info to par, to avoid diffs
  in drm, radeonkms and i915.

* While there, use drm_fb_helper_alloc_fbi() in drm/radeon as well for
  allocating the struct fb_info, and uncomment drm_fb_helper_release_fbi(),
  which is needed in an error handler there.