drm/i915: Update queue_flip() to take a request structure

Updated the display page flip code to do explicit request creation and
submission rather than relying on the OLR and just hoping that the request
actually gets submitted at some random point.

The sequence is now to create a request, queue the work to the ring, assign the
known request to the flip queue work item then actually submit the work and post
the request.

Note that every single flip function used to finish with
'__intel_ring_advance(ring);'. However, immediately after they return there is
now an add request call which will do the advance anyway. Thus the many
duplicate advance calls have been removed.

v2: Updated commit message with comment about advance removal.

v3: The request can now be allocated by the _sync() code earlier on. Thus the
page flip path does not necessarily need to allocate a new request, it may be
able to re-use one.

For: VIZ-5115
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Tomas Elf <tomas.elf@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>