- add lock for single read and continuous read APIs
- update onetime read start singal delay for hardware limitation[*]
- move adc_caps to soc_caps.h
- update license dates
[*] There is a hardware limitation. If the APB clock frequency is high, the
step of this reg signal: ``onetime_start`` may not be captured by the
ADC digital controller (when its clock frequency is too slow). A rough
estimate for this step should be at least 3 ADC digital controller
clock cycle.
