vm: replace vm-region with address-space

address-space is a non-recursive data structure, which contains a flat list of vm_areas representing
mapped vm-objects.

userspace programs can no longer create sub-address-spaces. instead, they can reserve portions of
the address space, and use that reserved space to create mappings.

include/kernel/iovec.h

@@ -4,10 +4,12 @@
 #include <mango/types.h>
 #include <stddef.h>
 
+struct address_space;
+
 struct iovec_iterator {
 	/* if this is set, we are iterating over a list of iovecs stored in
 	 * userspace, and must go through this region to retrieve the data. */
-	struct vm_region *it_region;
+	struct address_space *it_region;
 	const kern_iovec_t *it_vecs;
 	size_t it_nr_vecs;
 	size_t it_vec_ptr;
@@ -22,7 +24,7 @@ extern void iovec_iterator_begin(
 	size_t nr_vecs);
 extern void iovec_iterator_begin_user(
 	struct iovec_iterator *it,
-	struct vm_region *address_space,
+	struct address_space *address_space,
 	const kern_iovec_t *vecs,
 	size_t nr_vecs);