freedreno/batch: always update last_fence

freedreno/batch: always update last_fence

Not all flush paths come thru fd_context_flush(), so we should also set
last_fence in the batch flush path.  This avoids some no-op flushes just
to get a fence.  For example when pctx->flush_resource() triggers a
flush.

We should probably keep the last_fence update in fd_context_flush() as
well to handle deferred flush case.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Eric Anholt <eric@anholt.net>