UPSTREAM: crypto: arm/chacha20 - always use vrev for 16-bit rotates

UPSTREAM: crypto: arm/chacha20 - always use vrev for 16-bit rotates

The 4-way ChaCha20 NEON code implements 16-bit rotates with vrev32.16,
but the one-way code (used on remainder blocks) implements it with
vshl + vsri, which is slower.  Switch the one-way code to vrev32.16 too.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
(cherry picked from commit 4e34e51f48ab7f77a4022aa810a786daa3eb3e22)
Bug: 112008522
Test: As series, see Ic61c13b53facfd2173065be715a7ee5f3af8760b
Change-Id: If6f8ea9545aa6ed0478e812d6e17400c186b003b
Signed-off-by: Eric Biggers <ebiggers@google.com>