[jdk11u-dev] RFR: 8270947: AArch64: C1: use zero_words to initialize all objects

[Xin Liu]

We would like to backport [JDK-8270947](https://bugs.openjdk.org/browse/JDK-8270947) to jdk11u. It's not only less code to maintain, but also better generated code. C1 can leverage DC ZVA in large allocations on aarch64. The secondary consideration is that openjdk11u aligns with oraclejdk11u. 

This isn't a clean backport. Small cosmetic changes are made in `MacroAssembler::zero_words(Register ptr, Register cnt)` chunk. 

There are also 2 trailing bugfixes. We will post them together.

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Commit messages:
 - Backport 6c68ce2d396c6fe02201daf2bdb8c164de807cc1

Changes: https://git.openjdk.org/jdk11u-dev/pull/1502/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1502&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8270947
  Stats: 28949 lines in 8 files changed: 28783 ins; 117 del; 49 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1502.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1502/head:pull/1502

PR: https://git.openjdk.org/jdk11u-dev/pull/1502