media: Documentation: ccs: Add user documentation for the CCS driver

Add user documentation for the CCS driver. This includes e.g. sub-devices
implemented by the driver.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>