[media] solo6x10: expose encoder quantization setting as V4L2 control

solo6*10 boards have configurable quantization parameter which takes
values from 0 to 31, inclusively.

This change enables setting it with ioctl VIDIOC_S_CTRL with id
V4L2_CID_MPEG_VIDEO_H264_MIN_QP.

Signed-off-by: Andrey Utkin <andrey.utkin@corp.bluecherry.net>
Signed-off-by: Ismael Luceno <ismael.luceno@corp.bluecherry.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>