se050/lpc55: Investigate execution times and I2C data rate

[robin-nitrokey]

Executing the full SE050 test suite on the NK3 takes much longer than on the NRF52 and the execution times have a high variance when running the test suite multiple times. On the NRF52, this can be reproduced by changing the I2C data rate from 400 kHz to 100 kHz. On the LPC55, we use 100 kHz per default, but changing to 400 kHz does not fix the problem.

See also the discussion starting here.