media: vivid: add number of HDMI ports to device state

This will be used for HDMI-specific controls such as hotplug detection
and power present.

Signed-off-by: Johan Korsnes <johan.korsnes@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>