drm/omap: tpd12s015: remove platform data support

All devices using tpd12s015 driver are doing DT boot. No need of further
supporting the platform data. This patch removes support for platform
data.

Signed-off-by: Manisha Agrawal <manisha.agrawal@ti.com>
[tomi.valkeinen@ti.com: minor adjustments]
Acked-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>