drm/i2c: tda998x: drop support for platform_data

After the commit 0fb2970b ("drm/armada: remove non-component
support") there are no remaining users of the struct
tda998x_encoder_params. Drop the header and corresponding API from the
TDA998x driver.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250113-drm-move-tda998x-v3-1-214e0682a5e4@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>