RFR: 8292640: C2: Remove unused scratch register usages on x86

[Vladimir Ivanov]

(PR is dependent on #9932.)

Remove redundant scratch register usages in C2 generated code on x86. 

Stubs put constants in code cache, so they are RIP-relative addressable from generated code. It allows to save on scratch registers when accessing constants.  

Testing: hs-tier1 - hs-tier4

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Depends on: https://git.openjdk.org/jdk/pull/9932

Commit messages:
 - redundant temps
 - movptr

Changes: https://git.openjdk.org/jdk/pull/9933/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9933&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292640
  Stats: 408 lines in 5 files changed: 22 ins; 29 del; 357 mod
  Patch: https://git.openjdk.org/jdk/pull/9933.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9933/head:pull/9933

PR: https://git.openjdk.org/jdk/pull/9933