Add tests for I2C timing, adjust SDADEL/SCLDEL

Tests from RM0433 and I2C specification (UM10204)

Adjust SDADEL/SCLDEL values slightly so they pass the tests in all cases. Changes:

Sm SCLDEL `i2cclk / 800_000 / presc - 1` -> `i2cclk / 500_000 / presc - 1`
Fm SDADEL `i2cclk / 8_000_000 / presc` -> `i2cclk / 4_000_000 / presc`
Fm+ SDADEL `2` -> `i2cclk / 8_000_000 / presc`

Author: richardeoin