drm/i915/gem: Give each object class a friendly name

Name the object classes and their offspring for easier lockdep
debugging.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200529183204.16850-2-chris@chris-wilson.co.uk