board: rockchip: rk35xx: Add device tree files to MAINTAINERS

Update MAINTAINERS files for RK3566/RK3568/RK3588 boards to include
related device tree files. Also replace space with tabs.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Acked-by: Eugen Hristev <eugen.hristev@collabora.com>