media: rcar-vin: Move hardware buffer tracking to own struct

To support SEQ_TB/BT not all buffers given to the hardware will be
equal, the driver needs to keep track of different buffer types. Move
the tracking of buffers given to hardware into a struct so additional
tracking fields can be associated with each buffer.

[hverkuil: fix small checkpatch warning]

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>