driver: uart: add wake-up support for uart device.

This CL configures the UART wake-up event triggered from a falling edge
(START condition) on CR_SIN pin. It also includes:

1. Introduce wui_maps property in yaml file to present relationship
   between Wake-Up Input (WUI) and UART device.
2. Implement wake-up mechanism by MIWU api functions.

Signed-off-by: Mulin Chao <MLChao@nuvoton.com>