sensor: fxos8700: add support for hardware reset pin

Add support for pulsing the hardware reset pin of the FXOS8700 high
during initialization.

According to the datasheet, this is required for the I2C/SPI bus
auto-detection logic to work properly if the VDD/VDDIO power
sequencing order cannot be guaranteed.

Signed-off-by: Henrik Brix Andersen <henrik@brixandersen.dk>