RFR: 8277627: Fix copyright years in some jvmci files

[Emanuel Peter]

Fixed copyright years from "xxxx, xxxx" to "xxxx" (if same year mentioned twice), according to copyright year specification.

Checked that tests are not affected.

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Commit messages:
 - 8277627: Fix copyright years in some jvmci files

Changes: https://git.openjdk.java.net/jdk/pull/6985/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6985&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277627
  Stats: 9 lines in 9 files changed: 0 ins; 0 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6985.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6985/head:pull/6985

PR: https://git.openjdk.java.net/jdk/pull/6985