[11u] RFR: 8256488: [aarch64] Use ldpq/stpq instead of ld4/st4 for small copies in StubGenerator::copy_memory

[Hohensee, Paul]

Please review this backport to 11u. The backport is clean except for a copyright update. It’s the first of two follow-ons from the backport of JDK-8255351: Add detection for Graviton 2 CPUs.

JBS: https://bugs.openjdk.java.net/browse/JDK-8256488
Patch: https://github.com/openjdk/jdk/commit/6e006223
Webrev: http://cr.openjdk.java.net/~phh/8256488/webrev.11u.00/

Thanks,
Paul