drm/tilcdc: Use devm_kzalloc() and devm_kcalloc() for private data

Use devm_kzalloc() and devm_kcalloc() for private data allocation at
driver load time.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>