iio: test: Mark file local structure arrays static.

Warning cleanup:
drivers/iio/test/iio-test-rescale.c:32:30: warning: symbol 'scale_cases' was not declared. Should it be static?
drivers/iio/test/iio-test-rescale.c:480:30: warning: symbol 'offset_cases' was not declared. Should it be static?

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220807145457.646062-2-jic23@kernel.org

iio: afe: rescale: export symbols used during testing

In preparation for module support, export symbols use during testing.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Link: https://lore.kernel.org/r/20220710013109.3349104-5-liambeguin@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: test: rescale: add MODULE_* information

In preparation for module support, add missing MODULE_* information.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Link: https://lore.kernel.org/r/20220710013109.3349104-2-liambeguin@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: test: add basic tests for the iio-rescale driver

The iio-rescale driver supports various combinations of scale types and
offsets. These can often result in large integer multiplications. Make
sure these calculations are done right by adding a set of kunit test
cases that build on top of iio-test-format.

To run these tests, add the following to .kunitconfig
$ cat .kunitconfig
CONFIG_IIO=y
CONFIG_IIO_RESCALE_KUNIT_TEST=y
CONFIG_KUNIT=y

Then run:
$ ./tools/testing/kunit/kunit.py run --kunitconfig .kunitconfig

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220213025739.2561834-7-liambeguin@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>