RFR: 8257143: Enable JVMCI code installation tests on AArch64

[Nick Gasson]

This set of jtreg tests test JVMCI code installation independently of
Graal. Currently they only run on x86 as the minimal assembler required
is only implemented for that platform. This patch implements the
TestAssembler for AArch64 to ensure JVMCI test coverage even if the
Graal embedded in OpenJDK is disabled/removed.

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Commit messages:
 - 8257143: Enable JVMCI code installation tests on AArch64

Changes: https://git.openjdk.java.net/jdk/pull/1475/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1475&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257143
  Stats: 573 lines in 10 files changed: 556 ins; 0 del; 17 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1475.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1475/head:pull/1475

PR: https://git.openjdk.java.net/jdk/pull/1475