RFR: 8288012: AArch64: unnecessary macro expansion in stubGenerator_aarch64

[Hao Sun]

We use utility routines to replace macros in generate_md5_implCompress
and generate_sha512_implCompress() functions, as these macro expanisons
would bloat the generator.

Minor update: "Label keys" is removed since it's dead code.

In my local "release + server" build on AArch64 machine, the size of
stubGenerator_aarch64.o is reduced about 9% (from 6.73 MB to 6.13 MB).

Testings:
Tier1~3 passed on sha512 feature supporting machine.
We evaluted JMH test case MessageDigests.java and didn't see viable
performance change with and without this patch.

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Commit messages:
 - 8288012: AArch64: unnecessary macro expansion in stubGenerator_aarch64

Changes: https://git.openjdk.org/jdk/pull/10058/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10058&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288012
  Stats: 272 lines in 1 file changed: 96 ins; 72 del; 104 mod
  Patch: https://git.openjdk.org/jdk/pull/10058.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10058/head:pull/10058

PR: https://git.openjdk.org/jdk/pull/10058