Add assembler helper to calculate PMF timestamp offset

Given the service name and timestamp id, this assembler macro
calculates the offset into a memory region where the per-cpu timestamp
value is located.

Change-Id: I47f6dfa2a17be182675e2ca0489d6eed42433209
diff --git a/include/lib/pmf/pmf_helpers.h b/include/lib/pmf/pmf_helpers.h
index 1b8c507..9be6050 100644
--- a/include/lib/pmf/pmf_helpers.h
+++ b/include/lib/pmf/pmf_helpers.h
@@ -69,8 +69,8 @@
 /*
  * Convenience macro to allocate memory for a PMF service.
  */
-#define PMF_ALLOCATE_TIMESTAMP_MEMORY(_name, _total_id)			\
-	static unsigned long long pmf_ts_mem_ ## _name[_total_id]	\
+#define PMF_ALLOCATE_TIMESTAMP_MEMORY(_name, _total_id)		\
+	unsigned long long pmf_ts_mem_ ## _name[_total_id]	\
 	__section("pmf_timestamp_array") __used;
 
 /*