hugefileobj: rewrite page allocation/handling

* manage pages by an array
* fix mmap of fd created by memfd_create() populates the map
* refactor pgsize and pgshift handling

Change-Id: Icaf015b10afc35f2b95f93059adf1a1b6b92e14e
refs: #1475

kernel/include/pager.h

@@ -33,6 +33,7 @@ struct pager_create_result {
 	int		maxprot;
 	uint32_t flags;
 	size_t size;
+	int pgshift;
 	char path[PATH_MAX];
 };