UPSTREAM: [media] videodev2.h: Extend struct v4l2_ext_controls

UPSTREAM: [media] videodev2.h: Extend struct v4l2_ext_controls

So it can be used to get the default value of a control.

Without this change it is not possible to get the
default value of array controls.

Change-Id: I4370b7f2a40a08f28648f8dcaa3d84405db12523
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Alpha Lin <alpha.lin@rock-chips.com>
(cherry picked from commit 35ec2a2fa5a362b07b590ae1568dc35e47a7b846)