mb1232.c: add distance iio sensor with i2c

Add I2CXL-MaxSonar ultrasonic distance sensors of types mb1202, mb1212,
mb1222, mb1232, mb1242, mb7040, mb7137 using an i2c interface

Implemented functionality:
- reading the distance via in_distance_raw
- buffered mode with trigger
- make use of interrupt to announce completion of ranging

Add mb1232 driver to Kconfig and Makefile

Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>