allowFlashWhileRunning() -> mcuCanFlashWhileRunning() - true if MCU
can flash while continue code execution. Dual bank mode on STM32.
New allowFlashWhileRunning() return true if MCU can write its own
flash while keep runnig OR settings are stored in external storage.
* Rename EFI_INTERNAL_FLASH to EFI_STORAGE_INT_FLASH
This define enables use of RE custom flash driver for storing
settings to internal flash.
* at_start_f435: enable MFS for settings storing in internal flash
* MRE: fix special build
* kinetis: fix flash_int.cpp vs flash_int.c mess
* at32: allow allowFlashWhileRunning()
* flash_main: supress warning