drm/i915: add gen7_render_ring_flush

For now, just a copy of gen6_render_ring_flush. Different gens have
different workarounds, so we want different functions.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc drivers/gpu/drm/i915/intel_ringbuffer.c
Simple merge