drm/i915: Additional request structure tracing

Added the request structure's 'uniq' identifier to the trace information. Also
renamed the '_complete' trace event to '_notify' as it actually happens in the
IRQ 'notify_ring()' function. The intention is to add a new '_complete' trace
event which occurs when a request structure is actually marked as complete.
However, at the moment the completion status is re-tested every time the query
is made so there isn't a completion event as such.

v2: New patch added to series.

v3: Rebased to remove completion caching as that is apparently contentious.

Change-Id: Ic9bcde67d175c6c03b96217cdcb6e4cc4aa45d67
For: VIZ-4377
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Thomas Daniel <Thomas.Daniel@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>