drm/nouveau: incorporate I2C TV encoder drivers

Chrontel CH7006 and Silicon Image sil164 drivers use drm_encoder_slave
interface which is being used only by the nouveau driver. It doesn't
make sense to keep this interface inside the DRM subsystem. In
preparation to moving this set of helpers to the nouveau driver, move
the only two I2C driver that use that interface to the nouveau driver
too.

Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250106-nouveau-encoder-slave-v3-1-1d37d2f2c67f@linaro.org