[aarch64-port-dev ] RFR: aarch64: minor improvements of atomic operations

[Yangfei (Felix)]

.
> 
> Is there a reason to not reopen this bug:
> 
> JDK-8233912 aarch64: minor improvements of atomic operations
> https://bugs.openjdk.java.net/browse/JDK-8233912
> 
> Dan
> 

Reopend and modified problem description on that bug.
Webrev: http://cr.openjdk.java.net/~fyang/8233912/webrev.00/
The webrev also adds one comment from aph.  
Passed tier1 & 2 & 3 test.  Also run jcstress test.  Will do the push.

Thanks,
Felix