RFR: 8247645: ChaCha20 intrinsics [v2]

[Jamil Nimeh]

> This PR delivers ChaCha20 intrinsics that accelerate the core block function that generates key stream from the key, counter and nonce.  Intrinsics have been written for the following platforms and instruction sets:
> 
> - x86_64: AVX, AVX2 and AVX512
> - aarch64: platforms that support the advanced SIMD instructions
> 
> Note: Microbenchmark results moved to a comment in the PR so we don't have to see it in every email.
> 
> Special thanks to the folks who have made many helpful comments while this PR was in draft form.

Jamil Nimeh has updated the pull request incrementally with six additional commits since the last revision:

 - Change intrinsic helper method name conform to convention
 - consolidate chacha macroAssembler routines into chacha stubGenerator file
 - More indentation fixes on aarch64
 - rename chapoly->chacha for macro file
 - rename chacha macro file to be consistent with x86_64 naming
 - Fix indentation issues

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/7702/files
  - new: https://git.openjdk.org/jdk/pull/7702/files/c79abe34..53b432e5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=7702&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=7702&range=00-01

  Stats: 826 lines in 9 files changed: 212 ins; 254 del; 360 mod
  Patch: https://git.openjdk.org/jdk/pull/7702.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/7702/head:pull/7702

PR: https://git.openjdk.org/jdk/pull/7702