ARM: dts: sun8i: Add Reduced Serial Bus controller device node to A23/A33 dtsi

This patch adds a device node for the Reduced Serial Bus (RSB)
controller and the defacto pinmux setting to the A23/A33 dtsi.

Since there is only one possible pinmux setting for RSB, just
set it in the dtsi.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>