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/sei610/MAINTAINERS b/board/amlogic/sei610/MAINTAINERS
index da77aaf..092178b 100644
--- a/board/amlogic/sei610/MAINTAINERS
+++ b/board/amlogic/sei610/MAINTAINERS
@@ -5,3 +5,4 @@
 F:	board/amlogic/sei610/
 F:	configs/sei610_defconfig
 F:	include/configs/sei610.h
+F:	doc/board/amlogic/sei610.rst