To improve performance on cores with deep pipelines such as ThunderX2,
reimplement gcm(aes) using a 4-way interleave rather than the 2-way
interleave we use currently.

This comes down to a complete rewrite of the GCM part of the combined
GCM/GHASH driver, and instead of interleaving two invocations of AES
with the GHASH handling at the instruction level, the new version
uses a more coarse grained approach where each chunk of 64 bytes is
encrypted first and then ghashed (or ghashed and then decrypted in
the converse case).

The core NEON routine is now able to consume inputs of any size,
and tail blocks of less than 64 bytes are handled using overlapping
loads and stores, and processed by the same 4-way encryption and
hashing routines. This gets rid of most of the branches, and avoids
having to return to the C code to handle the tail block using a
stack buffer.

The table below compares the performance of the old driver and the new
one on various micro-architectures and running in various modes.

        |     AES-128      |     AES-192      |     AES-256      |
 #bytes | 512 | 1500 |  4k | 512 | 1500 |  4k | 512 | 1500 |  4k |
 -------+-----+------+-----+-----+------+-----+-----+------+-----+
    TX2 | 35% |  23% | 11% | 34% |  20% |  9% | 38% |  25% | 16% |
   EMAG | 11% |   6% |  3% | 12% |   4% |  2% | 11% |   4% |  2% |
    A72 |  8% |   5% | -4% |  9% |   4% | -5% |  7% |   4% | -5% |
    A53 | 11% |   6% | -1% | 10% |   8% | -1% | 10% |   8% | -2% |
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>