drm/i915/trace: Remove engine out of the context sandwich

In the string tracepoint representation we ended up with the engine
sandwiched between context hardware id and context fence id.

Move the two pieces of context data together for redability.

Binary records are left as is, that is both fields remaing under the
existing name and ordering.

v2:
 * Do not consolidate the printk format, just reorder. (Lionel)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180525082642.18246-2-tvrtko.ursulin@linux.intel.com