drm/i915/gt: Move the [class][inst] lookup for engines onto the GT

To maintain a fast lookup from a GT centric irq handler, we want the
engine lookup tables on the intel_gt. To avoid having multiple copies of
the same multi-dimension lookup table, move the generic user engine
lookup into an rbtree (for fast and flexible indexing).

v2: Split uabi_instance cf uabi_class
v3: Set uabi_class/uabi_instance after collating all engines to provide a
stable uabi across parallel unordered construction.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com> #v2
Link: https://patchwork.freedesktop.org/patch/msgid/20190806124300.24945-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_context.c

@@ -70,6 +70,7 @@
 #include <drm/i915_drm.h>
 
 #include "gt/intel_lrc_reg.h"
+#include "gt/intel_engine_user.h"
 
 #include "i915_gem_context.h"
 #include "i915_globals.h"
@@ -1729,7 +1730,7 @@ get_engines(struct i915_gem_context *ctx,
 
 		if (e->engines[n]) {
 			ci.engine_class = e->engines[n]->engine->uabi_class;
-			ci.engine_instance = e->engines[n]->engine->instance;
+			ci.engine_instance = e->engines[n]->engine->uabi_instance;
 		}
 
 		if (copy_to_user(&user->engines[n], &ci, sizeof(ci))) {