sandbox: Only read the state if we have a state file

We should not read this unless requested. Make it conditional on the
option being provided.

Add some debugging to show the state being written.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/cpu/state.c b/arch/sandbox/cpu/state.c
index fcc0028..e38bb24 100644
--- a/arch/sandbox/cpu/state.c
+++ b/arch/sandbox/cpu/state.c
@@ -521,6 +521,7 @@
 			printf("Failed to write sandbox state\n");
 			return -1;
 		}
+		log_debug("Wrote state to file '%s'\n", state->ram_buf_fname);
 	}
 
 	/* Delete this at the last moment so as not to upset gdb too much */