[media] solo6x10: clean up motion detection handling

An earlier patch temporarily disabled regional motion detection. This patch
adds it back: the 'Motion Detection Enable' control is now a 'Motion Detection Mode'.
And to set/get the regional thresholds two new ioctls were added to get/set those
thresholds.
The BUF_FLAG constants were also updated to prevent clashing with existing buffer
flags.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>