media: dw9807: Add dw9807 vcm driver

DW9807 is a 10 bit DAC from Dongwoon, designed for linear
control of voice coil motor.

This driver creates a V4L2 subdevice and
provides control to set the desired focus.

Signed-off-by: Alan Chiang <alanx.chiang@intel.com>
Signed-off-by: Andy Yeh <andy.yeh@intel.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>