[NFC] Extract X86MCInstLower::LowerMachineOperand.
[NFC] Extract X86MCInstLower::LowerMachineOperand.

Summary: Refactoring-only change that will be used later.

Reviewers: reames, atrick

Reviewed By: atrick

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D10196

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@239739 91177308-0d34-0410-b5e6-96231b3b80d8

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