media: staging: rkisp1: improve documentation of rkisp1-common.h

Add more detailed documentation of the structs and functions
in rkisp1-common.h
Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Acked-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/staging/media/rkisp1/TODO

@@ -2,7 +2,6 @@
 * Fix checkpatch errors.
 * Review and comment every lock
 * Handle quantization
-* Document rkisp1-common.h
 * streaming paths (mainpath and selfpath) check if the other path is streaming
 in several places of the code, review this, specially that it doesn't seem it
 supports streaming from both paths at the same time.