[omworld-jdk] RFR: 8326752: Lilliput: OMCache: Add cache lookup unrolling

[Axel Boldt-Christmas]

Implement unrolling of OM cache lookups in C2 so experiments and an evaluation can be performed.

Adds `OMC2UnrollCacheLookup`, `OMC2UnrollCacheLookupLoopTail` and `OMC2UnrollCacheEntires` flags which can be tuned cache lookup unrolling in C2. 

`OMC2UnrollCacheLookup` will unroll up to `OMC2UnrollCacheEntires` (depending on `OMCacheSize`) and if `OMC2UnrollCacheLookupLoopTail` is set and entries are left the rest of the cache will be checked.

All of these flags are temporary to allow for evaluation of the cache lookup in C2 (size and unrolling). See issue JDK-8326759

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Commit messages:
 - Add flags for unrolled cache lookup in C2

Changes: https://git.openjdk.org/lilliput/pull/139/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=139&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326752
  Stats: 219 lines in 5 files changed: 142 ins; 58 del; 19 mod
  Patch: https://git.openjdk.org/lilliput/pull/139.diff
  Fetch: git fetch https://git.openjdk.org/lilliput.git pull/139/head:pull/139

PR: https://git.openjdk.org/lilliput/pull/139