ARM: dts: sun5i: Add PWM channel 0 pinmux setting for A13/A10s

Add a pinmux setting for the first pwm channel. This is often used for
backlight dimming on tablets.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>