e580d22f4a
Also, re-enable calibration storage for CircuitPlayground Express. Tested with a 500hz PWMOut on Metro M0 with Saleae: * with crystal 500hz * with usb 500hz +- 0.1hz * without either 487hz += 0.1hz SAMD51 is skipped due to DFLL errata and the fact it defaults to a factory calibrated 48mhz that works fine for USB. Fixes #648