This patch optimizes Poly1305 for powerpc64 architecture by utilizing POWER9-specific instruction
vmsumudm for full 64-bit multiplication applied on single block based on radix 2^64
The patch also adds new option
--enable-power9 for configuration to compile Power ISA v3.0 code.
testsuite passes all tests of this patch.
Benchmark of poly1305 update using nettle-benchmark on Power9
|472.63 Mbyte/s||657.47 Mbyte/s|