cifs: Use iterate_and_advance*() routines directly for hashing

Replace the bespoke cifs iterators of ITER_BVEC and ITER_KVEC to do hashing
with iterate_and_advance_kernel() - a variant on iterate_and_advance() that
only supports kernel-internal ITER_* types and not UBUF/IOVEC types.

The bespoke ITER_XARRAY is left because we don't really want to be calling
crypto_shash_update() under the RCU read lock for large amounts of data;
besides, ITER_XARRAY is going to be phased out.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Tom Talpey <tom@talpey.com>
cc: Enzo Matsumiya <ematsumiya@suse.de>
cc: linux-cifs@vger.kernel.org
Link: https://lore.kernel.org/r/20240814203850.2240469-24-dhowells@redhat.com/

 # v2
Signed-off-by: Christian Brauner <brauner@kernel.org>