RFR: 8284813: x86 Code cleanup related to move instructions.

[Jatin Bhateja]

Summary of changes:

- Correct feature checks in some assembler move instruction.
- Explicitly pass opmask register in routines accepting merge argument.
- Code re-organization related to move instruction, pull out the merge argument up to instruction pattern or top level caller.
- Add missing encoding based move elision checks in some macro assembly routines.

Kindly review and share your feedback.

Regards,
Jatin

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Commit messages:
 - 8284813: x86 Code cleanup related to move instructions.

Changes: https://git.openjdk.java.net/jdk/pull/8230/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8230&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284813
  Stats: 188 lines in 8 files changed: 37 ins; 66 del; 85 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8230.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8230/head:pull/8230

PR: https://git.openjdk.java.net/jdk/pull/8230