Sample Code for KL46 UART0 wakeup from VLPS

1. Tested on FRDM-KL46 with external 32.768k crystal replacing original
8M crystal;
2. Two cases of UART0 wakeup mode are tested, including Edge interrupt
mode and data received interrupt mode;
3. IDLE line function for data package received is added;
4. The project is build with IAR.