MAINTAINERS: Update addresses for TI display drivers

Update the maintainer email addresses for TI display drivers.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Jyri Sarha <jyri.sarha@iki.fi>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201216075917.17481-1-tomi.valkeinen@ti.com