RFR: 8235748: ZGC: Remove ZAddress::address()

[Per Liden]

I propose that we remove ZAddress::address(). It was useful for the now 
defunct Sparc port, but none of the currently supported architectures 
need it. Should we ever need it in the future, we can easily add it again.

Removing ZAddress::address() implies also removing ZAddressBase and the 
initialization functions ZPlatformAddressBase().

Bug: https://bugs.openjdk.java.net/browse/JDK-8235748
Webrev: http://cr.openjdk.java.net/~pliden/8235748/webrev.0

/Per