power: VNDK Compliance change for 8996 target.

Added pthread header file for avoiding compilation issue
while enabling VNDK on msm8996 target.

Change-Id: Ia90b4407721650bde907369e1a40ba996737bafe
diff --git a/power-8996.c b/power-8996.c
index 0b1c362..8afb266 100644
--- a/power-8996.c
+++ b/power-8996.c
@@ -40,6 +40,7 @@
 #include <utils/Log.h>
 #include <hardware/hardware.h>
 #include <hardware/power.h>
+#include <pthread.h>
 
 #include "utils.h"
 #include "metadata-defs.h"