mm: added page fault range caching for each mm_space_t

mm: added last_pagefault handling when mm_space_t is unmapped

mm: fixed styling inconsistencies, fixed last pagefault range removal

mm: fix unitialized last_pagefault member in slab data

kernel-src/include/kernel/mm.h

@@ -46,6 +46,8 @@ typedef struct {
 	rbtree_t *ranges;
 	void *start;
 	void *end;
+
+	mm_range_t *last_pagefault;
 } mm_space_t;
 
 typedef struct {