RFR: Cherry-pick: 8204941: Refactor TemplateTable::_new to use MacroAssembler helpers for tlab and eden

[Roman Kennke]

Subject says it all. It reduces our upstream footprint a little bit, but
primarily this is meant to make Roland's life easier with merging some
conflicting C2 changesets.

See:
http://mail.openjdk.java.net/pipermail/shenandoah-dev/2018-June/006565.html

Webrev:
http://cr.openjdk.java.net/~rkennke/cherrypick-8204941/webrev.00/

Testing: tier3_gc_shenandoah ok

Ok?

Roman