MAINTAINERS: Add maintainer for TI LCDC DRM driver

Add Jyri Sarha as tilcdc maintainer and Tomi Valkeinen as reviewer.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Jyri Sarha <jsarha@ti.com>