[media] vidioc-g-edid.xml: be explicit about zeroing the reserved array

The G/S_EDID documentation did not explicitly state that the reserved array
should be zeroed by the application.

Also add the missing VIDIOC_SUBDEV_G/S_EDID ioctl names to the header.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>