drm/i915: Restore marking context objects as dirty on pinning

Commit e8a9c58fcd ("drm/i915: Unify active context tracking between
legacy/execlists/guc") converted the legacy intel_ringbuffer submission
to the same context pinning mechanism as execlists - that is to pin the
context until the subsequent request is retired. Previously it used the
vma retirement of the context object to keep itself pinned until the
next request (after i915_vma_move_to_active()). In the conversion, I
missed that the vma retirement was also responsible for marking the
object as dirty. Mark the context object as dirty when pinning
(equivalent to execlists) which ensures that if the context is swapped
out due to mempressure or suspend/hibernation, when it is loaded back in
it does so with the previous state (and not all zero).

Fixes: e8a9c58fcd ("drm/i915: Unify active context tracking between legacy/execlists/guc")
Reported-by: Dennis Gilmore <dennis@ausil.us>
Reported-by: Mathieu Marquer <mathieu.marquer@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99993
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100181
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: <drm-intel-fixes@lists.freedesktop.org> # v4.11-rc1
Link: http://patchwork.freedesktop.org/patch/msgid/20170322205930.12762-1-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1440,6 +1440,8 @@ static int intel_ring_context_pin(struct intel_engine_cs *engine,
 		ret = context_pin(ctx);
 		if (ret)
 			goto error;
+
+		ce->state->obj->mm.dirty = true;
 	}
 
 	/* The kernel context is only used as a placeholder for flushing the