media: adv7180: Add optional reset GPIO

There is a reset input that can be controlled by GPIO. Let's add it
to let the driver control it if required.

[hverkuil: fix a small checkpatch alignment warning]

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>