RFR: 8321808: G1: Use unsigned type for non-negative G1 flags

[Albert Mingkun Yang]

Simple type update for some G1 flags.

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Commit messages:
 - g1-uint-globals

Changes: https://git.openjdk.org/jdk/pull/17063/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17063&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321808
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/17063.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17063/head:pull/17063

PR: https://git.openjdk.org/jdk/pull/17063