mspm0: provide cross-MCU BUSCLK configurator/calculator #4445
Description
BUSCLK is a configurable clock source for different peripheral devices and it's configured differently across MSPM0 series. To configure peripheral devices, it's important to know exact baud rate of BUSCLK.
There is naive attempt to calculate BUSCLK in embassy-mspm0/src/i2c.rs::calculate_clock_rate which must be extended and made available as a common mspm0 functionality.