boards/afcz: more verbose clock diagnostics + reduce Si57X gain to avoid intermittent clock glitches during vco tuning

rxts_calibrator: increase t24p tollerance to 2ns to avoid recalibrating with minor t24p offsets (~200ps seen in sis83k)

softpll: 'source tracking' mode for aux clocks (observe phase shift between local WR clock and a number of external clocks)