FROMGIT: media: v4l2-ctrls: Add average QP control

Add a control V4L2_CID_MPEG_VIDEO_AVERAGE_QP to report the average QP
value of the current encoded frame. The value applies to the last
dequeued capture buffer.

Signed-off-by: Ming Qian <ming.qian@nxp.com>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Sebastian Fricke <sebastian.fricke@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

Bug: 352213761
(cherry picked from commit 62096c48
https://git.linuxtv.org/media_tree.git

 master)
Change-Id: I0d8af1997a1a3f0b658f2fb917026092b5d9f5e5
Signed-off-by: Zhipeng Wang <zhipeng.wang_1@nxp.com>