UPSTREAM: crypto: arm64/aes-xctr - Improve readability of XCTR and CTR modes

Added some clarifying comments, changed the register allocations to make
the code clearer, and added register aliases.

Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
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 c0eb7591)
Change-Id: I173a03b39591efa5337c4f2c0a79bf32205df9fa
Signed-off-by: Nathan Huckleberry <nhuck@google.com>