drm/i915: Move the decision to use the breadcrumb tasklet to the backend

drm/i915: Move the decision to use the breadcrumb tasklet to the backend

Use the engine->flags to store whether we want to kick the submission
tasklet on receipt of a breadcrumb interrupt, so that this decision can
be made by the submission backend and not dependent on a limited feature
test within the interrupt handler. This should make it easier to adapt to
different submission backends.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Xiaolin Zhang <xiaolin.zhang@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190329154912.13781-1-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>