V4L/DVB (13238): v4l2_subdev: rename tuner s_standby operation to core s_power

Upcoming I2C v4l2_subdev drivers need a way to control the subdevice
power state from the core. This use case is already partially covered by
the tuner s_standby operation, but no way to explicitly come back from
the standby state is available.

Rename the tuner s_standby operation to core s_power, and fix tuner
drivers accordingly. The tuner core will call s_power(0) instead of
s_standby(). No explicit call to s_power(1) is required for tuners as
they are supposed to wake up from standby automatically.

[mchehab@redhat.com: CodingStyle fix]
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>