Add option to STM32CubeMX: do not (re)generate MX_*_Init() functions

I welcome do not regenerate main() in new CubeMX, this is very good for bootloaders. My main is also boot_main, I had to rename it everytime after project was regenerated.

My suggestion is please add this functionality for every MX_*_Init function. Not generate function call already present, but I mean this for function.

Eg: Somewhere I have uart initialized with baudrate loaded from flash, and I would not like to everytime replace newly generated init function with my edited one. Same applies for RTC when somebody uses backup register in MX_RTC_Initfunction.

Any thoughts?