linux-imx

[media] v4l2-subdev.h: Improve documentation

This header were poorly documented, and weren't using the
kernel-doc format. Document everything but the macros using
the right format.

While here, also fix the other comments to match the
Linux CodingStyle.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>