Tweak Keccak for small speed-up

* cipher/keccak_permute_32.h (KECCAK_F1600_PERMUTE_FUNC_NAME): Track
rounds with round constant pointer instead of separate round counter.
* cipher/keccak_permute_64.h (KECCAK_F1600_PERMUTE_FUNC_NAME): Ditto.
(KECCAK_F1600_ABSORB_FUNC_NAME): Tweak lanes pointer increment for bulk
absorb loops.

Patch makes small tweaks to improve performance.

Benchmark on Intel Haswell @ 3.2 Ghz:

Before:

|  nanosecs/byte   mebibytes/sec   cycles/byte

SHAKE128 | 2.27 ns/B 420.5 MiB/s 7.26 c/B
SHAKE256 | 2.79 ns/B 341.4 MiB/s 8.94 c/B
SHA3-224 | 2.64 ns/B 361.7 MiB/s 8.44 c/B
SHA3-256 | 2.79 ns/B 341.4 MiB/s 8.94 c/B
SHA3-384 | 3.65 ns/B 261.3 MiB/s 11.68 c/B
SHA3-512 | 5.27 ns/B 181.0 MiB/s 16.86 c/B

After:

|  nanosecs/byte   mebibytes/sec   cycles/byte

SHAKE128 | 2.25 ns/B 423.5 MiB/s 7.21 c/B
SHAKE256 | 2.77 ns/B 343.9 MiB/s 8.88 c/B
SHA3-224 | 2.62 ns/B 364.1 MiB/s 8.38 c/B
SHA3-256 | 2.77 ns/B 343.8 MiB/s 8.88 c/B
SHA3-384 | 3.63 ns/B 262.6 MiB/s 11.63 c/B
SHA3-512 | 5.23 ns/B 182.3 MiB/s 16.75 c/B

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