board: rockchip: rk35xx: Add myself as reviewer to MAINTAINERS

Add myself as a reviewer for RK3566/RK3568/RK3588 boards that I have and
can help with review and testing of defconfig and device tree changes.

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