stm32h7-i2c chooses timing based on SoC model, not board

[cbiffle]

The current configure_timing routine in stm32h7-i2c assumes that any board with a given SoC model has the same clock configuration.

hubris/drv/stm32h7-i2c/src/lib.rs

Line 193 in 7adbded

fn configure_timing(&self, i2c: &RegisterBlock) {

Knowledge of clocks should probably move out of this crate to the caller, who should decide it based on target_board instead.

FYI @bcantrill