RFR: 8285683: Missing @ since 11 in java.security.spec.MGF1ParameterSpec fields

[Bradford Wetmore]

Two new constant fields `MGF1ParameterSpec.SHA512_224` and `MGF1ParameterSpec.SHA512_256` didn't have `@since 11` tag added as part of [JDK-8146293](https://bugs.openjdk.java.net/browse/JDK-8146293). 

This bug addresses this issue.

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Commit messages:
 - 8285683: Missing @ since 11 in java.security.spec.MGF1ParameterSpec fields

Changes: https://git.openjdk.java.net/jdk/pull/8411/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8411&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285683
  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8411.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8411/head:pull/8411

PR: https://git.openjdk.java.net/jdk/pull/8411