RFR: 8330026: Serial: Move some includes to vmStructs_serial.hpp

[Albert Mingkun Yang]

Trivial moving some Serial related headers.

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Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/18718/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18718&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330026
  Stats: 4 lines in 2 files changed: 2 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/18718.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18718/head:pull/18718

PR: https://git.openjdk.org/jdk/pull/18718