Request for reviews (M): 6954029: Improve implicit null check generation with compressed oops

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/6954029/webrev

Fixed 6954029: Improve implicit null check generation with compressed oops

Problem:
When DecodeN instruction does not fold into address expression
it may prevent implicit null check generation if it is scheduled
below the null check since the corresponding memory instruction
could not be moved.

Solution:
If needed move DecodeN instruction before null check to generate
implicit null check.

I also removed code which switch off default COOP usage on N1:
currently generated COOP code perform better on N1 (tested jbb2005).