Add ARMv7/NEON implementation of Keccak

* cipher/Makefile.am: Add 'keccak-armv7-neon.S'.
* cipher/keccak-armv7-neon.S: New.
* cipher/keccak.c (USE_64BIT_ARM_NEON): New.
(NEED_COMMON64): Select if USE_64BIT_ARM_NEON.
[NEED_COMMON64] (round_consts_64bit): Rename to...
[NEED_COMMON64] (_gcry_keccak_round_consts_64bit): ...this; Add
terminator at end.
[USE_64BIT_ARM_NEON] (_gcry_keccak_permute_armv7_neon)
(_gcry_keccak_absorb_lanes64_armv7_neon, keccak_permute64_armv7_neon)
(keccak_absorb_lanes64_armv7_neon, keccak_armv7_neon_64_ops): New.
(keccak_init) [USE_64BIT_ARM_NEON]: Select ARM/NEON implementation
if supported by HW.
* cipher/keccak_permute_64.h (KECCAK_F1600_PERMUTE_FUNC_NAME): Update
to use new round constant table.
* configure.ac: Add 'keccak-armv7-neon.lo'.

Patch adds ARMv7/NEON implementation of Keccak (SHAKE/SHA3). Patch
is based on public-domain implementation by Ronny Van Keer from
SUPERCOP package:
https://github.com/floodyberry/supercop/blob/master/crypto_hash/\
keccakc1024/inplace-armv7a-neon/keccak2.s

Benchmark results on Cortex-A8 @ 1008 Mhz:

Before (generic 32-bit bit-interleaved impl.):

|  nanosecs/byte   mebibytes/sec   cycles/byte

SHAKE128 | 83.00 ns/B 11.49 MiB/s 83.67 c/B
SHAKE256 | 101.7 ns/B 9.38 MiB/s 102.5 c/B
SHA3-224 | 96.13 ns/B 9.92 MiB/s 96.90 c/B
SHA3-256 | 101.5 ns/B 9.40 MiB/s 102.3 c/B
SHA3-384 | 131.4 ns/B 7.26 MiB/s 132.5 c/B
SHA3-512 | 189.1 ns/B 5.04 MiB/s 190.6 c/B

After (ARM/NEON, ~3.2x faster):

|  nanosecs/byte   mebibytes/sec   cycles/byte

SHAKE128 | 25.09 ns/B 38.01 MiB/s 25.29 c/B
SHAKE256 | 30.95 ns/B 30.82 MiB/s 31.19 c/B
SHA3-224 | 29.24 ns/B 32.61 MiB/s 29.48 c/B
SHA3-256 | 30.95 ns/B 30.82 MiB/s 31.19 c/B
SHA3-384 | 40.42 ns/B 23.59 MiB/s 40.74 c/B
SHA3-512 | 58.37 ns/B 16.34 MiB/s 58.84 c/B

• Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>