The code already got unwieldy and we want to dump more per-ring
registers.

Only functional change is that we now also capture the video
ring registers on ilk.

v2: fixup a refactor fumble spotted by Chris Wilson.
Reviewed-by: NEugeni Dodonov <eugeni.dodonov@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>