TI RS232 level shifter additional modem control lines through gpio

Required properties:
- compatible: ti,trs3386
- gpios: list of the gpios matching the mctrl lines, specify <0> if not used
	0: DTR
	1: RTS
	2: DSR
	3: RI
	4: OUT1
	5: OUT2
  NOTEs:
	- the RTS gpio is not required if the UART has a dedicated RTS output
	- <0> entries at the end can be left out
- uart: the uart the tr3386 is connected to for RX/TX

example:

        trs3386 {
                compatible = "ti,trs3386";
                uart = <&uart3>;	/* trs3386 is connected to uart3 */
		gpios = <&gpio1 21 0>,	/* DTR: GPIO_21 */
			<0>;		/* RTS: unused */
        }
