iio: pressure: bmp280: add reset GPIO line handling

On the APQ8060 Dragonboard the reset line to the BMP085 pressure
sensor is not deasserted on boot, so the driver needs to handle
this. For a simple GPIO line supplied as a descriptor (from a board
file, device tree or ACPI) this does the trick.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>