Request for reviews (S): 6984368 Large default heap size does not allow to use zero based compressed oops

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/6984368/webrev

Fixed 6984368: Large default heap size does not allow to use zero based compressed oops

The heap size expression in max_heap_for_compressed_oops()
does not take into account HeapBaseMinAddress value which
is used to get zero based compressed oops.

Also MaxPermSize is rounded up in CollectorPolicy::initialize_flags()
which makes invalid all expressions which use it before rounding.