RFR: 8282621: G1: G1SegmentedArray remove unnecessary template parameter

[Ivan Walulya]

Hi all,

Please review this refactoring change to remove unnecessary template parameters. The change has two commits, one to remove the template parameter, this allows for the second clean up to hoist `G1CardSetAllocator` parameter independent methods and variables into a base class.

Testing: Tier 1.

-------------

Commit messages:
 - hoist parameter independent methods into a base class
 - Remove slote template parameter

Changes: https://git.openjdk.java.net/jdk/pull/7689/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7689&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282621
  Stats: 117 lines in 5 files changed: 47 ins; 31 del; 39 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7689.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7689/head:pull/7689

PR: https://git.openjdk.java.net/jdk/pull/7689