orangefs: Provide a splice-read wrapper

Provide a splice_read wrapper for ocfs2.  This increments the read stats
and then locks the inode across the call to filemap_splice_read() and a
revalidation of the mapping.  Splicing from direct I/O is done by the
caller.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Jens Axboe <axboe@kernel.dk>
cc: Mike Marshall <hubcap@omnibond.com>
cc: Martin Brandenburg <martin@omnibond.com>
cc: devel@lists.orangefs.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-block@vger.kernel.org
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/20230522135018.2742245-24-dhowells@redhat.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>