[vector] RFR 8219878: Vectorized Poly1305 benchmark

[Adam Petcher]

webrev: https://cr.openjdk.java.net/~apetcher/8219878/webrev.00/
JBS: https://bugs.openjdk.java.net/browse/JDK-8219878

I have another crypto benchmark ready for review. This time it's 
Poly1305, which is a symmetric authenticator that is typically combined 
with ChaCha20 to produce authenticated encryption. I tested this 
benchmark with a slightly modified JVM containing a multiplication 
optimization[1]. Without this optimization, the performance of this 
vectorized implementation on AVX2 is not much better than the scalar 
implementation of Poly1305 in the JDK.

The webrev also includes some changes to the ChaCha20 benchmark which 
were necessary to get it to compile after some Vector API changes.


[1] https://bugs.openjdk.java.net/browse/JDK-8219881