ringbuffer: Make ring buffer access irq-save

We have to temporarily disable nterrupts when performing rinbuffer
operations, as the ring buffer is used both from IRQ as well as process
context.

firmware/src_simtrace/card_emu.c

@@ -17,6 +17,8 @@
  *
  */
 
+#define TRACE_LEVEL 6
+
 #include <assert.h>
 #include <errno.h>
 #include <string.h>