This allows a board configuration to select which kind of averaging
should be applied to the pin instead of always using 32 sample average.
Very high impedance sources may need to disable hardware averaging in
order to give correct values, the on-chip temperature sensor is one such
signal source.
Uses timer freerunning counter mode (TFC) and updating an internal
reference point instead of relying on RTT for reference time. The
target accuracy has been greatly improved for all test cases in
bench_periph_timer
