kill off the NuttX ADC driver config; we're not going to use it
First cut at a simple® ADC driver built on our driver framework.
Cleanup and add support for multiple channels.
Enable the temperature sensor channel for F2/F4 devices.
Configure ADC GPIOs on IO
Add trivial ADC support to PX4IO.
Add ADC measurements and reporting to PX4IO, including calibration for the battery input.
Introduced battery_status uORB topic, changed sensors app to publish to it, extended px4io driver to publish to it. Both do only so if the battery voltage is reasonably high, at 3.3V
Fixed stupid copy/paste typo
Merge branch 'master' of github.com:PX4/Firmware into px4io-adc-integration-battery-msg
Merged latest master
Merge pull request #130 from PX4/px4io-adc-integration-battery-msg

Enables the PX4IO ADC (from px4io-adc-integration branch)