RFR: 8233797: ZGC: Unify naming convention for functions using atomics

[Erik Österlund]

Hi,

Functions in ZGC that use atomics sometimes have an _atomic postfix in 
the name, and sometimes not. This enhancement is about unifying that. 
The proposal is to remove the _atomic postfix in situations where there 
is no non-atomic counterpart.

This patch applies on top of 8233061.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8233797

Webrev:
http://cr.openjdk.java.net/~eosterlund/8233797/webrev.00/

Thanks,
/Erik