drm/i915: Give names to more ring registers

The logical render context population has a bunch of raw ring register
offsets. Use the names we have for them, and in cases where we we don't,
give them names.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1446672017-24497-23-git-send-email-ville.syrjala@linux.intel.com


Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>