ecryptfs: Provide a splice-read wrapper

Provide a splice_read wrapper for ecryptfs to update the access time on the
lower file after the operation.  Splicing from a direct I/O fd will update
the access time when ->read_iter() is called.

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: Tyler Hicks <code@tyhicks.com>
cc: ecryptfs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-block@vger.kernel.org
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/20230522135018.2742245-18-dhowells@redhat.com


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