kernel: implement cpu IDs and per-cpu variables

include/socks/percpu.h

@@ -1,6 +1,7 @@
 #ifndef SOCKS_PERCPU_H_
 #define SOCKS_PERCPU_H_
 
+#include <socks/status.h>
 #include <socks/compiler.h>
 
 #define DEFINE_PERCPU_VAR(type, name) \
@@ -10,6 +11,7 @@
 
 #define percpu_put(var)
 
+extern kern_status_t init_per_cpu_areas(void);
 extern void *__percpu_get(void *var);
 
 #endif