RFR: 8307907: [ppc] Remove RTM locking implementation [v2]

[Martin Doerr]

> This PR removes RTM code for PPC64. The instructions are not supported by Power10 processors.
> The situation is even worse in Power9 compatibility mode on Power10. The VM detects RTM to be available, but the processor is unable to complete any transaction successfully.
> The feature had so many problems and we never supported it in production.

Martin Doerr has updated the pull request incrementally with one additional commit since the last revision:

  Remove RTM from feature string. Otherwise, tests complain about it.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14398/files
  - new: https://git.openjdk.org/jdk/pull/14398/files/33189a38..97f8d07f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14398&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14398&range=00-01

  Stats: 36 lines in 2 files changed: 0 ins; 35 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14398.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14398/head:pull/14398

PR: https://git.openjdk.org/jdk/pull/14398