RFR(M): tweak zeroing elimination to support initialization of non flattened value arrays

[Tobias Hartmann]

Hi Roland,

very nice! Here are some questions:
- Could you explain the change to vm_version_x86.cpp?
- I'm a bit confused by DefaultValue and RawDefaultValue. It seems that the code in
graphKit.cpp:4051 only sets RawDefaultValue but there are asserts that check that if DefaultValue is
not set, RawDefaultValue should not be set either (for example, in memnode.cpp).
- What does "coops" stand for? Maybe add a comment to that method.

This solves JDK-8189802 [1], right? If so, I would suggest that you re-use this bug number.

Thanks,
Tobias

[1] https://bugs.openjdk.java.net/browse/JDK-8189802