RFR: 8256166: [C2] Registers get confused on Big Endian after 8221404

[Martin Doerr]

C2 crashes with broken register encoding on Big Endian platforms after JDK-8221404 was pushed.
Reason is that int values "_RM_I" are pairwise swapped on 64 bit Big Endian platforms.

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Commit messages:
 - 8256166: [C2] Registers get confused on Big Endian after 8221404

Changes: https://git.openjdk.java.net/jdk/pull/1165/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1165&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256166
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1165.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1165/head:pull/1165

PR: https://git.openjdk.java.net/jdk/pull/1165