media: atmel: atmel-isc: extract CBC submodule config into separate function

The CBC submodule is a part of the atmel-isc pipeline, and stands for
Contrast Brightness Control. It is used to apply gains and offsets to the
luma (Y) and chroma (U, V) components of the YUV elements.
The CBC submodule should be initialized in the product specific driver
as it's product specific. Other products can implement it differently

[hverkuil: made isc_sama5d2_config_cbc static]

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>