RFR: 8255351: Add detection for Graviton 1 & 2 CPUs

[Eugene Astigeevich]

This commit adds detection for Graviton 1 (as Cortex-A72) and for Graviton 2 (as Neoverse N1) and enables UseSIMDForMemoryOps for them.

The patch passed jtreg tier1-2 and all gtest tests with linux-aarch64-server-release build.

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Commit messages:
 - 8255351: Add detection for Graviton 1 & 2 CPUs

Changes: https://git.openjdk.java.net/jdk/pull/1315/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1315&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255351
  Stats: 14 lines in 1 file changed: 14 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1315.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1315/head:pull/1315

PR: https://git.openjdk.java.net/jdk/pull/1315