[media] media: Doc s5p-mfc add missing fields to s5p_mfc_dev structure definition

Add missing documentation for s5p_mfc_dev structure definition.

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>