RFR: 8222467: ZGC: Log min/max/softmax capacity

[Per Liden]

With the newly added -XX:SoftMaxCapacity and the upcoming JEP 351 
(Uncommit Unused Memory), it's interesting to know the heap 
min/max/softmax capacity, which is currently not logged.

This patch adds that logging. It also moves and renames the string 
format macros, so that we can reuse ZSIZE_FMT/ARGS for the new logging.

Bug: https://bugs.openjdk.java.net/browse/JDK-8222467
Webrev: http://cr.openjdk.java.net/~pliden/8222467/webrev.0

/Per