kernel: don't use typedef for enums or non-opaque structs

vm/model.c

@@ -1,13 +1,13 @@
 #include <socks/vm.h>
 
-static vm_model_t model;
+static enum vm_model model;
 
-vm_model_t vm_memory_model(void)
+enum vm_model vm_memory_model(void)
 {
 	return model;
 }
 
-void vm_set_memory_model(vm_model_t m)
+void vm_set_memory_model(enum vm_model m)
 {
 	model = m;
 }