drm/i915: trace vm eviction instead of everything

Tracing vm eviction is really the event we care about. For the cases we
evict everything, we still will get the trace.

v2: Add the drm device to the trace since we might not be the only
device in the system. (Chris)

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>