drm/i915: Enable resource streamer bits on MI_BATCH_BUFFER_START

Adds support for enabling the resource streamer on the legacy
ringbuffer for HSW and GEN8.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>