Previously the end of the heap was the start (lowest address) of the stack.
With the changes in this commit these addresses are now independent,
allowing a board to place the heap and stack in separate locations.
The pin alternate function information is derived from ST's datasheet
https://www.st.com/resource/en/datasheet/stm32l432kc.pdf
In the datasheet, the line 2 of AF4 includes I2C2 but actually the chip
does not have I2C2 so it is removed.