ARM: sun5i: dt: Move uart3 pinctrl node to common DTSI

The uart3 pins are shared between the A10s and A13, move the pinctrl node
to the common DTSI to avoid duplication.

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>