sha/asm/keccak1600-armv8.pl: halve the size of hw-assisted subroutine.

Yes, it's second halving, i.e. it's now 1/4 of original size, or more
specifically inner loop. The challenge with Keccak is that you need
more temporary registers than there are available. By reversing the
order in which columns are assigned in Chi, it's possible to use
three of A[][] registers as temporary prior their assigment.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7294)