Add support for suspend and resume by stopping and starting the video
pipeline while still retaining all buffers given to the driver by
user-space and internally allocated ones, this gives the application a
seamless experience.

Buffers are never returned to user-space unprocessed so user-space don't
notice when suspending. When resuming the driver restarts the capture
session using the internal scratch buffer, this happens before
user-space is unfrozen, this leads to speedy response times once the
application resumes its execution.

As the entire pipeline is stopped on suspend all subdevices in use are
also stopped, and if they enter a shutdown state when not streaming
(such as the R-Car CSI-2 driver) they too will be suspended and resumed
in sync with the VIN driver.

To be able to do keep track of which VINs should be resumed a new
internal state SUSPENDED is added to recode this.
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>