block: convert bounce, q->bio_split to bioset_init()/mempool_init()

Convert the core block functionality to embedded bio sets.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 98b175c..5e472fc 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -760,6 +760,11 @@ struct biovec_slab {
 	struct kmem_cache *slab;
 };
 
+static inline bool bioset_initialized(struct bio_set *bs)
+{
+	return bs->bio_slab != NULL;
+}
+
 /*
  * a small number of entries is fine, not going to be performance critical.
  * basically we just need to survive