media: v4l2-ctrls: add v4l2_ctrl_modify_dimensions

Add a new function to modify the dimensions of an array control.

This is typically used if the array size depends on e.g. the currently
selected video format.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>