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/p212/MAINTAINERS b/board/amlogic/p212/MAINTAINERS
index 8848df0..cae6994 100644
--- a/board/amlogic/p212/MAINTAINERS
+++ b/board/amlogic/p212/MAINTAINERS
@@ -8,3 +8,7 @@
 F:	configs/libretech-ac_defconfig
 F:	configs/libretech-cc_defconfig
 F:	configs/p212_defconfig
+F:	doc/board/amlogic/p212.rst
+F:	doc/board/amlogic/libretech-ac.rst
+F:	doc/board/amlogic/libretech-cc.rst
+F:	doc/board/amlogic/khadas-vim.rst