ParallelScavengeHeap::initialize() passes GenAlignment as page size to os::trace_page_sizes instead of actual page size

Using GenAlignment as the page size like this is wrong:
os::trace_page_sizes("Heap",
                       MinHeapSize,
                       reserved_heap_size,
                       GenAlignment,
                       heap_rs.base(),
                       heap_rs.size());

We should instead pass in the correct "os" page size used. It might make sense to add some additional log that logs the different alignments used by parallel, because I think this is the only place the GenAlignment is printed.