sunxi: Add initial support for R40

The R40 is the successor to the A20. It is a hybrid of the A20, A33
and the H3.

The R40's PIO controller is compatible with the A20,
Reuse the A20 UART and I2C muxing code by adding the R40's macro.

The display pipeline is the newer DE 2.0 variant.
Block enabling video on R40 for now.

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