[media] videodev2.h: add COLORSPACE_RAW

V4L2_COLORSPACE_RAW is added for raw image formats where the picture
is minimally processed and is in the internal colorspace of the sensor.

This is typically used in digital cameras where the image processing is
done later.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>