RFR: Get easy on template instantiations in ShConcMark

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/concmark-less-templates/webrev.01/

Turns out, we don't need all these recursive template instantiation for all arguments. We are fine
with only those arguments that would end up in mark_loop_work. This improves build times, and .o/.so
file sizes a bit. This does not degrade performance, because the important part is mark_loop_work,
and we specialize it enough.

Testing: hotspot_gc_shenandoah, eyeballing inline trees

Thanks,
-Aleksey