splice: divorce the splice structure/function definitions from the pipe header

We need to move even more stuff into the header so that folks can use
the splice_to_pipe() implementation instead of open-coding a lot of
pipe knowledge (see relay implementation), so move to our own header
file finally.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

fs/nfsd/vfs.c

@@ -23,7 +23,7 @@
 #include <linux/file.h>
 #include <linux/mount.h>
 #include <linux/major.h>
-#include <linux/pipe_fs_i.h>
+#include <linux/splice.h>
 #include <linux/proc_fs.h>
 #include <linux/stat.h>
 #include <linux/fcntl.h>