media: add V4L2_CTRL_TYPE_AREA control type

This type contains the width and the height of a rectangular area.

Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Ricardo Ribalda Delgado <ribalda@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>