MAINTAINERS: Add myself as a reviewer for rockchip drm

As I am familiar with all the details of vop2 display
architecture, I can help review and test all related
changes in this subsystem, so add my email here to make
sure I get CC'd on rockchip drm changes.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20231211120023.1785687-1-andyshrk@163.com