RFR: 8252898: remove bulk registration of JFR CompilerPhaseType names

[Doug Simon]

The changes made in [JDK-8193210](https://bugs.openjdk.java.net/browse/JDK-8193210) support only [bulk
registration](https://github.com/openjdk/jdk/blob/4e6a4af1866d0007d368b78bf78b6a8e1c8be425/src/hotspot/share/compiler/compilerEvent.hpp#L75)
of compiler phase names with JFR. However, Graal only registers compiler phase names upon first execution of the phase
since the set of phases is not known during VM initialization. This means registration of a Graal phase name needs to
do unnecessary work, wrapping a single name into an array to conform to the bulk registration API. This pull request
updates the registration API to be in terms of a registering a single phase name.

-------------

Commit messages:
 - 8252898: remove bulk registration of JFR CompilerPhaseType names

Changes: https://git.openjdk.java.net/jdk/pull/77/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=77&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252898
  Stats: 114 lines in 6 files changed: 31 ins; 41 del; 42 mod
  Patch: https://git.openjdk.java.net/jdk/pull/77.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/77/head:pull/77

PR: https://git.openjdk.java.net/jdk/pull/77