RFR: 8256476: Assert in vmIntrinsics::flags_for with -XX:+Verbose

[Ioi Lam]

Please review this trivial fix.

The bug was introduced by [JDK-8254855](https://bugs.openjdk.java.net/browse/JDK-8254855). `log2_FLAG_LIMIT` [1] is changed from 4 to 3. So the hard-coded value 15 in `vmIntrinsics::flags_for()` should be changed to 7.

[1] https://github.com/openjdk/jdk/blame/0570cc10b579580f37b8978f2498459bdd4c870b/src/hotspot/share/classfile/vmIntrinsics.hpp#L1043

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Commit messages:
 - 8256476: Assert in vmIntrinsics::flags_for with -XX:+Verbose

Changes: https://git.openjdk.java.net/jdk/pull/1270/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1270&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256476
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1270.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1270/head:pull/1270

PR: https://git.openjdk.java.net/jdk/pull/1270