FROMGIT: media: v4l2-ctrls: Add encoder constant quality control

When V4L2_CID_MPEG_VIDEO_BITRATE_MODE value is
V4L2_MPEG_VIDEO_BITRATE_MODE_CQ, encoder will produce
constant quality output indicated by
V4L2_CID_MPEG_VIDEO_CONSTANT_QUALITY control value.
Encoder will choose appropriate quantization parameter
and bitrate to produce requested frame quality level.

Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>

Bug: 151414336
Change-Id: Ifc29387620ad0c164acf81e0320f5d28072dcd61
(cherry picked from commit ecc6e684128db22b89c0cc955e10de24c4163f6e
 https://git.linuxtv.org/svarbanov/media_tree.git

 venus-for-next-v5.10)
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>