drm/i915/trace: Describe engines as class:instance pairs

drm/i915/trace: Describe engines as class:instance pairs

Instead of using the engine->id, use uabi_class:instance pairs in trace-
points including engine info.

This will be more readable, more future proof and more stable for
userspace consumption.

v2:
 * Use u16 for class and instance. (Chris Wilson)

Signed-off-by: Tvrtko Ursulin <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: [email protected]
Reviewed-by: Chris Wilson <[email protected]>
Reviewed-by: Lionel Landwerlin <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]