robert-hh fd7b57dd22 samd/mphalport: Use CYCCNT for SAMD51's mp_hal_ticks_cpu().
And use mp_hal_ticks_us() for SAM21's mp_hal_ticks_cpu().  The SAMD21 has
no CYCCNT register, and the SysTick register has only a 1 ms span (== 48000
count range).
2022-10-06 22:59:02 +11:00
..