MFC r315272, r315370
Implement INHERIT_ZERO for minherit(2).
INHERIT_ZERO is an OpenBSD feature.
When a page is marked as such, it would be zeroed
This would be used in new arc4random(3) functions.
The adj_free and max_free values of new_entry will be calculated and
assigned by subsequent vm_map_entry_link(), therefore, remove the
Submitted by: alc