remove rt_passed_second in clock; init device driver when driver has been opened if it is not in activate status; change interrupt nest count to rt_uint8_t; add rt_console_set_device function in kservice.c (rt_kprintf function can use device right now)

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@464 bbd45198-f89e-11dd-88c7-29a3b14d5316