ARM: dts: colibri-vf: Add pinmux for UART_0 aka UART_A RTS/CTS pins

Add pinmux for UART_A RTS, CTS pin's.

Signed-off-by: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
Acked-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>