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.

kernel/iovec.c

@@ -1,7 +1,7 @@
+#include <kernel/address-space.h>
 #include <kernel/iovec.h>
 #include <kernel/libc/string.h>
 #include <kernel/util.h>
-#include <kernel/vm-region.h>
 
 static bool read_iovec(
 	struct iovec_iterator *it,
@@ -18,7 +18,7 @@ static bool read_iovec(
 	}
 
 	size_t nr_read = 0;
-	kern_status_t status = vm_region_read_kernel(
+	kern_status_t status = address_space_read(
 		it->it_region,
 		(virt_addr_t)it->it_vecs + (index * sizeof(kern_iovec_t)),
 		sizeof(kern_iovec_t),
@@ -30,7 +30,7 @@ static bool read_iovec(
 
 void iovec_iterator_begin_user(
 	struct iovec_iterator *it,
-	struct vm_region *region,
+	struct address_space *region,
 	const kern_iovec_t *vecs,
 	size_t nr_vecs)
 {