btrfs: move struct io_ctl into ctree.h and rename it

We'll need to put the io_ctl into the block_group cache struct, so
name it struct btrfs_io_ctl and move it into ctree.h

Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 6bf16d5..e305ccd 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1256,6 +1256,17 @@
 	atomic_t count;
 };
 
+struct btrfs_io_ctl {
+	void *cur, *orig;
+	struct page *page;
+	struct page **pages;
+	struct btrfs_root *root;
+	unsigned long size;
+	int index;
+	int num_pages;
+	unsigned check_crcs:1;
+};
+
 struct btrfs_block_group_cache {
 	struct btrfs_key key;
 	struct btrfs_block_group_item item;