RFR: 8277137: Set OnSpinWaitInst/OnSpinWaitInstCount defaults to "isb"/1 for Arm Neoverse N1 [v3]

[Evgeny Astigeevich]

> One `ISB` implementation of `Thread.OnSpinWait` shows performance improvements on Graviton2 (Arm Neoverse N1 implementation), e.g. https://github.com/openjdk/jdk/pull/5562#issuecomment-966153163. 
> 
> Testing:
> - `make test TEST=gtest`: Passed
> - `make run-test TEST=tier1`: Passed
> - `make run-test TEST=tier2`: Passed
> - `make run-test TEST=hotspot/jtreg/compiler/onSpinWait`: Passed

Evgeny Astigeevich has updated the pull request incrementally with one additional commit since the last revision:

  Set defaults for OnSpinWaitInst/OnSpinWaitInstCount independently

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6415/files
  - new: https://git.openjdk.java.net/jdk/pull/6415/files/56258906..a9edcca6

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6415&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6415&range=01-02

  Stats: 9 lines in 2 files changed: 5 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6415.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6415/head:pull/6415

PR: https://git.openjdk.java.net/jdk/pull/6415