Changes to LPC11uXX sleep behavior

See: https://github.com/mbedmicro/mbed/issues/143

- Removed interface disconnect for reasons in that issue
- Removed incorrect comments copy pasted from LPC1768
- Switched from deepsleep to power down (see that issue also)
- Only enable components after wakeup when they are currently running
- Only keep watchdog and brownout running when they are currently running