ARM: sun5i: dt: Add UART3 CTS and RTS pins

Add a separate pinctrl node for the UART3 CTS and RTS pins shared between
the A10s and A13.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>