RFR: 8297445: PPC64: Represent Registers as values [v2]

[Martin Doerr]

> The recent Register implementation uses wild pointer (including null pointer) dereferences which exhibit undefined behavior. We should migrate away from pointer-based representation of Register values as it was done for x86 ([JDK-8292153](https://bugs.openjdk.org/browse/JDK-8292153)). Problems exist when trying to build with GCC 11 ([JDK-8297426](https://bugs.openjdk.org/browse/JDK-8297426)).
> Note: Implicit conversion from `intptr_t` to `RegisterOrConstant` is no longer supported. That's why I had to replace some `add` instructions.

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

  Update Copyright years.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11297/files
  - new: https://git.openjdk.org/jdk/pull/11297/files/5af4a37b..fc905a96

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11297&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11297&range=00-01

  Stats: 10 lines in 9 files changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/11297.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11297/head:pull/11297

PR: https://git.openjdk.org/jdk/pull/11297