sunxi: add support for Banana Pi M2 Zero board

Banana Pi M2 Zero is a board by Sinovoip with Allwinner H2+ SoC, 16-bit
512MiB DDR3 memory, a MicroSD slot, two MicroUSB ports (one OTG and one
powering-only) and a miniHDMI port.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Jun Nie <jun.nie@linaro.org>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
[jagan: Fixed board MAINTAINERS file]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>