Add support for MPL3115 NXP pressure sensor.

Tested by reading temperature and pressure:

$ cat /sys/bus/iio/devices/iio:device0/in_temp_raw
$ cat /sys/bus/iio/devices/iio:device0/in_pressure_raw
Signed-off-by: NBreno Lima <breno.lima@nxp.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>