drm/i915: Drop verbose and archaic "ring" from our internal engine names

We pretty print the name of an engine in several places, mostly for
debug, but also in the GPU hang report. Using "ring" in the name is
archaic (we call those engines now to differentiate them from the
multiple rings of commands we execute on each engine), quite verbose and
often tautological. We run out of room in our GPU hang report for
instance if we have more than a couple of engines hung simultaneously.
Bit the bullet and update the strings to reflect the common internal names.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170330134820.12273-1-chris@chris-wilson.co.uk