drm/i915/execlists: Listen to COMPLETE context event not ACTIVE_IDLE

Since commit e1fee72c
Author: Oscar Mateo <oscar.mateo@intel.com>
Date:   Thu Jul 24 17:04:40 2014 +0100

    drm/i915/bdw: Avoid non-lite-restore preemptions

execlists has listened to (ACTIVE_IDLE | ELEMENT_SWITCH) for detecting
when one context completed and it either continued onto the next (in port
1) or idled. We would always see COMPLETE | ACTIVE_IDLE on the final
context-switch event, but on recent gen it appears that we now get
separate ACTIVE_IDLE and COMPLETE events. In particular, the ACTIVE_IDLE
events may not be coupled to a context (since it is a general state rather
than a specific context completion event).

v2: Update the history, execlists did originally start out by listening
to the COMPLETE event not ACTIVE_IDLE.
v3: Update preempt completion test to also use COMPLETE not ACTIVE_IDLE.

References: bspec/12255
References: https://bugs.freedesktop.org/show_bug.cgi?id=103800


Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Michal Winiarski <michal.winiarski@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Acked-by: Michel Thierry <michel.thierry@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171120123458.23242-1-chris@chris-wilson.co.uk