This removes the difference in the time.ticks_us() range between SAMD21 and
SAMD51.
The function mp_hal_ticks_us_64() is added and used for:
- SAMD51's mp_hal_ticks_us and mp_hal_delay_us().
For SAMD21, keep the previous methods, which are faster.
- mp_hal_ticks_ms() and mp_hal_tick_ms_64(), which saves some bytes
and removes a potential race condition every 50 days.
Also set the us-counter for SAMD51 to 16 MHz for a faster reading of the
microsecond value.
Note: With SAMD51, mp_hal_ticks_us_64() has a 60 bit range only, which is
still a long time (~36000 years).
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