[jdk21u-dev] RFR: 8342601: AArch64: Micro-optimize bit shift in copy_memory

[Dmitry Chuyko]

This is a clean backport of a small generated asm micro-optimization for copy_memory stub (zero-latency mov can be used when the shift is zero).

Testing: test/hotspot/jtreg/compiler/arraycopy, tier1,2 on linux-aarch64.

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Commit messages:
 - Backport 893266c48f26e089d0449d2c161b04430741970c

Changes: https://git.openjdk.org/jdk21u-dev/pull/1574/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1574&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342601
  Stats: 12 lines in 1 file changed: 8 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1574.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1574/head:pull/1574

PR: https://git.openjdk.org/jdk21u-dev/pull/1574