sunxi: maintainers: Add myself for the TBS A711

Support for that board got introduced recently without the maintainers
part. Let's fix that.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>