MAINTAINERS: Update Allwinner entry and add new maintainer

Add Chen-Yu Tsai as a co-maintainer to the ARM sunxi support.

While we are doing so, also update the entry for new SoCs.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>