media: dt-bindings: media: i2c: Document DW9768 bindings

Add DeviceTree Binding Documentation for Dongwoon Anatech DW9768
voice coil actuator.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dongchun Zhu <dongchun.zhu@mediatek.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>