Implement free() to finish buddy allocator

NOTES.md

@@ -7,10 +7,10 @@
   - The objects get created, but GSI lookup only uses the one at index 0
 - Slab allocator for kernel structures
 - mark kernel memory pages global
-- kernel allocator `free()`
 - lock `memory_manager` and `page_manager` structures
 - Serial out based on circular/bip biffer and interrupts, not spinning on
   `write_ready()`
+- Split out more code into kutil for testing
 
 
 - Device Tree