- system_power portion of drivers/adc split into a new standalone module (drivers/system_power)
- additional availability flags added to system_power.msg so we know what boards even support (previously certain flags were faked if not available)
- drivers/system_power scheduled at minimum rate by default, but now also scheduled immediately on any relevant GPIO events
- now instead of running at 100 Hz with heavily reduced logging we can run at a minimal rate, log at full rate, and catch relevant changes immediately
This PR is preliminary ground work for FMUv5.
PX4 does not use the NuttX adc driver. But used the same format
for the data returned by the nuttx ADC driver.
There was a fixme:in src/platforms/px4_adc.h "this needs to be
a px4_adc_msg_s type" With this PR the need for
src/platforms/px4_adc.h goes away as the driver drv_adc.h now
describes the px4_adc_msg_t.
