RFR: 8276976: Rename LIR_OprDesc to LIR_Opr

[Man Cao]

Hi all,

Can I have reviews for this mechanical renaming change as a follow up to https://bugs.openjdk.java.net/browse/JDK-8276453?

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Commit messages:
 - Rename LIR_OprDesc to LIR_Opr

Changes: https://git.openjdk.java.net/jdk/pull/6377/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6377&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276976
  Stats: 238 lines in 14 files changed: 0 ins; 9 del; 229 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6377.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6377/head:pull/6377

PR: https://git.openjdk.java.net/jdk/pull/6377