media: cec-gpio.txt: add v5-gpios for testing the 5V line

In order to debug the HDMI 5V line we need to add a new v5-gpios
property.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>