boards: amlogic: add Radxa Zero defconfig

Add a defconfig for the Radxa Zero SBC, using an Amlogic S905Y2 chip.

Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
[narmstrong: updated u200 MAINTAINERS & add missing CONFIG_SYS_LOAD_ADDR from defconfig]
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/board/amlogic/u200/MAINTAINERS b/board/amlogic/u200/MAINTAINERS
index 655cf64..73c73b1 100644
--- a/board/amlogic/u200/MAINTAINERS
+++ b/board/amlogic/u200/MAINTAINERS
@@ -5,4 +5,5 @@
 F:	board/amlogic/u200/
 F:	configs/u200_defconfig
 F:	configs/bananapi-m5_defconfig
+F:	configs/radxa-zero_defconfig
 F:	doc/board/amlogic/u200.rst