[MP1] Fix redefinition

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

cores/arduino/stm32/OpenAMP/rsc_table.c

@@ -29,7 +29,9 @@
 #define VRING_COUNT           2
 
 /* VirtIO rpmsg device id */
-#define VIRTIO_ID_RPMSG       7
+#ifndef VIRTIO_ID_RPMSG
+  #define VIRTIO_ID_RPMSG       7
+#endif
 
 #if defined (VIRTIO_LOG)
   extern char virtio_log_buffer[];