board: rk3288: add more DT files to MAINTAINERS

A number of rk3229/rk3288 DT files are synced from Linux.
Add a maintainer to look after them and to help with
review and testing.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/board/radxa/rock2/MAINTAINERS b/board/radxa/rock2/MAINTAINERS
index a697e68..5328fd7 100644
--- a/board/radxa/rock2/MAINTAINERS
+++ b/board/radxa/rock2/MAINTAINERS
@@ -1,6 +1,9 @@
 FIREFLY
 M:	Simon Glass <sjg@chromium.org>
 S:	Maintained
+F:	arch/arm/dts/rk3288-rock2-som.dtsi
+F:	arch/arm/dts/rk3288-rock2-square.dts
+F:	arch/arm/dts/rk3288-rock2-square-u-boot.dtsi
 F:	board/radxa/rock2
 F:	include/configs/rock2.h
 F:	configs/rock2_defconfig