buflib: Check the validity of of handles passed to buflib_get_data() in DEBUG builds.

Change-Id: Ic274bfb4a8e1a1a10f9a54186b9173dbc0faa4c8

firmware/kernel/pthread/mutex.c

@@ -0,0 +1,21 @@
+#include <pthread.h>
+#include "kernel.h"
+
+void mutex_init(struct mutex *m)
+{
+    pthread_mutexattr_t attr;
+    pthread_mutexattr_init(&attr);
+    pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
+    pthread_mutex_init(&m->mutex, &attr);
+    pthread_mutexattr_destroy(&attr);
+}
+
+void mutex_lock(struct mutex *m)
+{
+    pthread_mutex_lock(&m->mutex);
+}
+
+void mutex_unlock(struct mutex *m)
+{
+    pthread_mutex_unlock(&m->mutex);
+}