V4L/DVB (9321): v4l2-int-if: Define new power state changes

Use enum v4l2_power instead of int as second argument to
vidioc_int_s_power. The new functionality is that standby state is also
recognised.

Signed-off-by: Sakari Ailus <sakari.ailus@nokia.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>