media: i2c: dw9768: Add DW9768 VCM driver

Add a V4L2 sub-device driver for DW9768 voice coil motor,
providing control to set the desired focus via IIC serial interface.

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