Documentation: media: vivid.rst: update TODO list

The vivid driver supports media controller support for quite a long
time now, so drop that from the list.

Since commit 4c4dacb0 ("media: vivid: loopback based on
'Connected To' controls") making EDID changes causes correct signaling
to happen, but what is still missing is the 100 ms delay required before
signaling that there is an HPD. Modify this TODO item accordingly.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>