MAINTAINERS: Update Allwinner SoCs maintainers

Maxime is stepping down as a maintainer, I'll take more active role and
Samuel joined the team.

Maxime, thank you for your effort! Samuel, welcome!

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Acked-by: Samuel Holland <samuel@sholland.org>
Acked-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Link: https://lore.kernel.org/r/20220220210714.2484019-1-jernej.skrabec@gmail.com