core/mem: define internal types for pkg and shm pools

- to allow easier identification when doing operations over mem block

mem/meminfo.h

@@ -35,6 +35,8 @@
 #ifndef meminfo_h
 #define meminfo_h
 
+#define MEM_TYPE_SHM	0
+#define MEM_TYPE_PKG	1
 
 /** Memory information structure */
 struct mem_info{