board: amlogic: add board doc files to MAINTAINERS

Add the recently added reStructuredText board documentation in the
appropriate MAINTAINERS files.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/board/amlogic/u200/MAINTAINERS b/board/amlogic/u200/MAINTAINERS
index 5ae7f5e..8c23f9a 100644
--- a/board/amlogic/u200/MAINTAINERS
+++ b/board/amlogic/u200/MAINTAINERS
@@ -4,3 +4,4 @@
 L:	u-boot-amlogic@groups.io
 F:	board/amlogic/u200/
 F:	configs/u200_defconfig
+F:	doc/board/amlogic/u200.rst