UPSTREAM: crypto: xctr - Add XCTR support

Add a generic implementation of XCTR mode as a template.  XCTR is a
blockcipher mode similar to CTR mode.  XCTR uses XORs and little-endian
addition rather than big-endian arithmetic which has two advantages:  It
is slightly faster on little-endian CPUs and it is less likely to be
implemented incorrect since integer overflows are not possible on
practical input sizes.  XCTR is used as a component to implement HCTR2.

More information on XCTR mode can be found in the HCTR2 paper:
https://eprint.iacr.org/2021/1441.pdf



Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Bug: 233652475
Link: https://lore.kernel.org/linux-arm-kernel/20220520181501.2159644-4-nhuck@google.com/T/


(cherry picked from commit 17fee07a)
Change-Id: Idb978c32cfbe646c22b35798e1dfb01f8e08e5fd
Signed-off-by: Nathan Huckleberry <nhuck@google.com>