RFR: Gcm to 8

[Eric Caspole]

By accident these JMH were never made available for 8.

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Commit messages:
 - Fix copyright for new files
 - Remove KeyAgreementBench from 8
 - Add GCM to 8 that were only in 11 til now

Changes: https://git.openjdk.org/jmh-jdk-microbenchmarks/pull/10/files
 Webrev: https://webrevs.openjdk.org/?repo=jmh-jdk-microbenchmarks&pr=10&range=00
  Stats: 244 lines in 2 files changed: 244 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jmh-jdk-microbenchmarks/pull/10.diff
  Fetch: git fetch https://git.openjdk.org/jmh-jdk-microbenchmarks pull/10/head:pull/10

PR: https://git.openjdk.org/jmh-jdk-microbenchmarks/pull/10