iio: pressure: bmp280: BMP280 calibration to entropy

The BMP280/BME280 calibration data should also go into the
entropy pool, like we do for BMP180.

This just adds the temperature and pressure calibration, the
humidity calibration seems like too much annoying calls to
add.

Cc: Tomasz Duszynski <tduszyns@gmail.com>
Cc: Stefan Tatschner <stefan.tatschner@gmail.com>
Cc: Andreas Klinger <ak@it-klinger.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>