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

[Roman Kennke]

TemplateTable::_new (in x86) currently has its own implementation of
tlab and eden allocation paths, which are basically identical to the
ones in MacroAssembler::tlab_allocate() and
MacroAssembler::eden_allocate(). TemplateTable should use the
MacroAssembler helpers to avoid duplication.

The MacroAssembler version of eden_allocate() features an additional
bounds check to prevent wraparound of obj-end. I am not sure if/how that
can ever happen and if/how this could be exploited, but it might be
relevant. In any case, I think it's a good thing to include it in the
interpreter too.

The refactoring can be taken further: fold incr_allocated_bytes() into
eden_allocate() (they always come in pairs), probably fold
tlab_allocate() and eden_allocate() into a single helper (they also seem
to come in pairs mostly), also fold initialize_object/initialize_header
sections too, but 1. I wanted to keep this manageable and 2. I also want
to factor the tlab_allocate/eden_allocate paths into BarrierSetAssembler
as next step (which should also include at least some of the mentioned
unifications).

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

Passes tier1_hotspot

Can I please get a review?

Roman