aio: minor formatting fix

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>
aio: added configuration within platform data.

* Allows for different bit shifting for each platform.
* New functions added for obtaining this information
* mraa_adc_raw_bits
* mraa_adc_supported_bits

* Update board information to include this. AIO module changed to allow
* use of the new board data

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>