crypto: arm/crct10dif - Implement plain NEON variant

The CRC-T10DIF algorithm produces a 16-bit CRC, and this is reflected in
the folding coefficients, which are also only 16 bits wide.

This means that the polynomial multiplications involving these
coefficients can be performed using 8-bit long polynomial multiplication
(8x8 -> 16) in only a few steps, and this is an instruction that is part
of the base NEON ISA, which is all most real ARMv7 cores implement. (The
64-bit PMULL instruction is part of the crypto extensions, which are
only implemented by 64-bit cores)

The final reduction is a bit more involved, but we can delegate that to
the generic CRC-T10DIF implementation after folding the entire input
into a 16 byte vector.

This results in a speedup of around 6.6x on Cortex-A72 running in 32-bit
mode. On Cortex-A8 (BeagleBone White), the results are substantially
better than that, but not sufficiently reproducible (with tcrypt) to
quote a number here.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

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