blake: rewrite the cache system

Unlike other hash algos, blake256 compute the hash
with blocks of 64 bytes.

We can do the first part on the cpu, only the 4 last int32
are computed on gpu (including the tested nonce)

Previous method was also using this kind of cache with a crc.

Blake Hash Speed: +5%
Some work on data alignment

linux: add -march=native (we build it ourself)

+ remove unused vars