[jdk11u-dev] RFR: 8233743: AArch64: Make r27 conditionally allocatable

[Dmitry Chuyko]

This is a prerequisite for JDK-8242449.
JVMCI and ZGC parts from original patch are not necessary for 11u: JDK-8231754 was not backported - no need to revert, Z for aarch64 has not been backported.

Testing: tier1, tier2 (aarch64).

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Commit messages:
 - [PATCH] Backport e2644b70cfd7358d9c8cb22666c3a32876dcc8ff

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/136/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=136&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8233743
  Stats: 278 lines in 3 files changed: 69 ins; 172 del; 37 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/136.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/136/head:pull/136

PR: https://git.openjdk.java.net/jdk11u-dev/pull/136