Add a function (as well as a helper macro) to obtain the best size in a
list of device specific sizes. This helps writing drivers as well as
aligns interface behaviour across drivers.

The struct in which this information is contained in is typically specific
to the driver, therefore the existing function v4l2_find_nearest_format()
does not address the need.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>