Support up to 8 PMU counters

Change-Id: Ia470d230b4bce152f88ab735e0a2ad2cdba80226
diff --git a/kernel/ethosu_core_interface.h b/kernel/ethosu_core_interface.h
index d5bcb54..ef63c3b 100644
--- a/kernel/ethosu_core_interface.h
+++ b/kernel/ethosu_core_interface.h
@@ -35,7 +35,7 @@
 #define ETHOSU_CORE_BUFFER_MAX 16
 
 /** Maximum number of PMU counters to be returned for inference */
-#define ETHOSU_CORE_PMU_MAX 4
+#define ETHOSU_CORE_PMU_MAX 8
 
 #define ETHOSU_CORE_MSG_MAGIC 0x41457631
 #define ETHOSU_CORE_MSG_VERSION_MAJOR 0