hal: Include pthread.h

Doesn't compile without it.

Change-Id: Ia75404ee1fc735df58fa6f9922063fcf2cc2022d
diff --git a/hal/platform_info.c b/hal/platform_info.c
index e55b91d..9cfd760 100755
--- a/hal/platform_info.c
+++ b/hal/platform_info.c
@@ -41,6 +41,7 @@
 #include "platform_api.h"
 #include "audio_extn.h"
 #include <platform.h>
+#include <pthread.h>
 #include <math.h>
 #ifdef LINUX_ENABLED
 #include <float.h>