media: docs: Add V4L2_CAP_EDID

Add documentation for the new edid capability.

Signed-off-by: Erling Ljunggren <hljunggr@cisco.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Sebastian Fricke <sebastian.fricke@collabora.com>
Reviewed-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>