RFR: 8330693: Generational ZGC: Simplify ZAddress::finalizable_good and ZAddress::mark_good

[Guoxiong Li]

Hi all,

This patch simplifies the methods `ZAddress::finalizable_good` and `ZAddress::mark_good`, mainly removing the code which computes the `non_mark_prev_bits`.

The tests `make test-tier1_gc` passed locally. Thanks for taking the time to review.

Best Regards,
-- Guoxiong

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Commit messages:
 - JDK-8330693

Changes: https://git.openjdk.org/jdk/pull/18873/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18873&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330693
  Stats: 6 lines in 1 file changed: 0 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/18873.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18873/head:pull/18873

PR: https://git.openjdk.org/jdk/pull/18873