ARM: dts: sun8i: v3s: add pwm controller to v3s dts

The Allwinner V3s and V3 SoCs feature a pwm controller identical to the
one used in the Allwinner A20.
This commit adds it to the V3s dtsi.

Signed-off-by: Tobias Schramm <t.schramm@manjaro.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20210513203527.2072090-3-t.schramm@manjaro.org