[Add] software simulator add

labus/serial.cc

@@ -0,0 +1,10 @@
+#include <serial.hh>
+#include <common.h>
+
+Serial::Serial(size_t siz) : WRDevice(siz) {}
+
+void Serial::write(char *buf, size_t addr, size_t len) {
+  for (size_t i = 0; i < len; ++i)
+    putc(buf[i], stdout);
+  fflush(stdout);
+}