fix(rmm): fix MISRA C:2012 Rule 10.3 in lib & runtime

Signed-off-by: AlexeiFedorov <Alexei.Fedorov@arm.com>
Change-Id: If607bf37c82c5db40ce4a8771fd29739bffa8aa8
diff --git a/lib/realm/include/buffer.h b/lib/realm/include/buffer.h
index dc716de..8bab8bc 100644
--- a/lib/realm/include/buffer.h
+++ b/lib/realm/include/buffer.h
@@ -9,6 +9,7 @@
 #include <assert.h>
 #include <smc-rmi.h>
 #include <stdbool.h>
+#include <stddef.h>
 #include <utils_def.h>
 
 enum buffer_slot {
@@ -45,12 +46,12 @@
 bool ns_buffer_read(enum buffer_slot slot,
 		    struct granule *ns_gr,
 		    unsigned int offset,
-		    unsigned int size,
+		    size_t size,
 		    void *dest);
 bool ns_buffer_write(enum buffer_slot slot,
 		     struct granule *ns_gr,
 		     unsigned int offset,
-		     unsigned int size,
+		     size_t size,
 		     void *src);
 
 /*