drm/i915: Include priority and completed status in request in/out tracepoints

It is useful to see the priority as requests are coming in and completed
status as requests are coming out of the GPU.

To achieve this in a more readable way we need to abandon the common
request_hw tracepoint class.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180504115643.22437-1-tvrtko.ursulin@linux.intel.com