drm/i915: Rename engines to match their user interface

drm/i915: Rename engines to match their user interface

During engine setup, we may find that some engines are fused off causing
a misalignment between internal names and the instances seen by users,
e.g. (I915_ENGINE_CLASS_VIDEO_DECODE, 1) may be vcs2 in hardware.
Normally this is invisible to the user, but a few debug interfaces (and
our own internal tracing) use the original HW name not the name the user
would expect as formed from their class:instance tuple. Replace our
internal name with the uabi name for consistency with, for example, error
states.

v2: Keep the pretty printing of class name in the selftest

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111311
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190807110431.8130-1-chris@chris-wilson.co.uk