ARM: dts: am335x-baltos-ir5221: use dedicated RTS/CTS signals

Before "tty: Add software emulated RS485 support for 8250" patch Baltos devices
relied on MCTRL_GPIO framework to handle both modem signals and RS485 mode.

With emulated RS485 support for 8250 we can now use these pins as dedicated
RTS/CTS signals taking advantage of hardware flow control etc. when operating
in RS232 mode.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>