Support up to 8 PMU counters

Change-Id: Ia470d230b4bce152f88ab735e0a2ad2cdba80226
diff --git a/kernel/uapi/ethosu.h b/kernel/uapi/ethosu.h
index 3c0a983..903316d 100644
--- a/kernel/uapi/ethosu.h
+++ b/kernel/uapi/ethosu.h
@@ -62,7 +62,7 @@
 #define ETHOSU_FD_MAX                   16
 
 /* Maximum number of PMUs available */
-#define ETHOSU_PMU_EVENT_MAX             4
+#define ETHOSU_PMU_EVENT_MAX             8
 
 /****************************************************************************
  * Types