galileo: Implement main() function

This patch implements the main() function for Galileo platform. At this
moment, only Processes subsystem is enabled. After this patch we are
able to some rudimentary debugging to ensure that process thread from
applications are being indeed executed.

Once we properly support more Contiki subsystems, such as clock, ctimer,
etimer, and rtimer, we will add them to Galileo platform's main() as well.

platform/galileo/contiki-main.c

@@ -28,8 +28,17 @@
  * OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include "contiki.h"
+
 int
 main(void)
 {
+  process_init();
+  autostart_start(autostart_processes);
+
+  while(1) {
+    process_run();
+  }
+
   return 0;
 }