media: v4l2-ctrls: add change flag for when dimensions change

Add a new V4L2_EVENT_CTRL_CH_DIMENSIONS change flag that is issued
when the dimensions of an array change as a result of a
__v4l2_ctrl_modify_dimensions() call.

This will inform userspace that there are new dimensions.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>