drm/i915: reorder field in gem_request tracepoints

Let's make the order of the fields of the tracepoints involving gem
request match across i915. This makes userspace processing of
tracepoint a bit easier.

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171218151959.14073-2-lionel.g.landwerlin@intel.com