UPSTREAM: f2fs: Advertise encrypted casefolding in sysfs

Older kernels don't support encryption with casefolding. This adds
the sysfs entry encrypted_casefold to show support for those combined
features. Support for this feature was originally added by
commit 7ad08a58bf67 ("f2fs: Handle casefolding with Encryption")

Bug: 254441685
Fixes: 7ad08a58bf67 ("f2fs: Handle casefolding with Encryption")
Cc: stable@vger.kernel.org # v5.11+
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
(cherry picked from commit 4c039d5452691fe80260e4c3dd7b629a095bd0a7)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I0f2b85176ce19871f058c35ad26f181bf40f0567