Various updates to support dynamically starting drivers.

Output during initialization should be suppressed. Unless an error occurs.
Note that main() can now be main(int argc, char **argv) and arguments can
be passed when bringing up the driver.

drivers/floppy/floppy.c

@@ -309,7 +309,6 @@ PUBLIC void main()
   if ((s=sys_irqenable(&irq_hook_id)) != OK)
   	panic("FLOPPY", "Couldn't enable IRQs", s);
 
-  printf("FLOPPY: user-level floppy disk driver initialized\n");
   driver_task(&f_dtab);
 }