This patch optimizes Poly1305 for powerpc64 architecture by utilizing POWER9-specific instruction
vmsumudm for full 64-bit multiplication applied on 4-blocks at parallel based on radix 2^44
testsuite passes all tests of this patch.
Benchmark of poly1305 update using nettle-benchmark on Power9
|C||single block (2^64)||multi blocks (2^44)|
|472.63 Mbyte/s||658.45 Mbyte/s||2136.30 Mbyte/s|