- the timeout computation for the spurious IRQ test confused numerator
and denominator in a fraction
- the timeout offset between timer channels was hardcoded to 5000 from
when the timer was only tested with 1 MHz as frequency
- This resulted in slooooow test runs when running at slow
frequencies
- fix overflow handling in the spinning wait
- likely this would never overflow anyway assuming that
`timer_init()` resets the counter value, but let's not rely on
this and just fix the bug for good
If the feature periph_timer_query_freqs is provided, use the
corresponding function to iterate over all supported frequencies to
increase test coverage.
