RFR: 8343810: [s390x] is_uimm* methods should take unsigned arguments

[Amit Kumar]

trivial patch which just updates the argument datatype of `is_uimm*` methods, from `int64_t` to `uint64_t`.

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Commit messages:
 - int64_t -> uint64_t

Changes: https://git.openjdk.org/jdk/pull/21967/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21967&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343810
  Stats: 7 lines in 1 file changed: 0 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/21967.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21967/head:pull/21967

PR: https://git.openjdk.org/jdk/pull/21967