arm64/crypto: GHASH secure hash using ARMv8 Crypto Extensions

This is a port to ARMv8 (Crypto Extensions) of the Intel implementation of the
GHASH Secure Hash (used in the Galois/Counter chaining mode). It relies on the
optional PMULL/PMULL2 instruction (polynomial multiply long, what Intel call
carry-less multiply).

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>