Try requests are now only supported by format processing pad operations
implemented by the driver.  The driver selection API operations
currently respond to them with -EINVAL.  While that is correct, it
constraints video device drivers to not use subdevice cropping at all
while processing user requested active frame size, otherwise their set
try format results might differ from active.  As a consequence, we
can't fix set format pad operation as not to touch crop rectangle since
that would affect users not being able to set arbitrary frame sizes.
Moreover, without a working set try selection support we are not able
to use pad config crop rectangle as a reference while processing set
try format requests.

Implement missing try selection support.  Moreover, as it will be now
possible to maintain the pad config crop rectangle via selection API,
start using it instead of the active one as a reference while
processing set try format requests.

is_unscaled_ok() helper, now also called from set selection operation,
has been just moved up in the source file to avoid a prototype, with no
functional changes.

[Sakari Ailus: Rebase on subdev state patches]

Fixes: 717fd5b4 ("[media] v4l2: replace try_mbus_fmt by set_fmt")
Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>