sd: prompt user for formatting if format is not VFAT compatible

[asi345]

This commit inserts a check to validate whether the sdcard where the backup will be put is VFAT compatible or not. VFAT compatilibity is crucial for using the card and lack of it could result in errors in the firmware. Therefore, when setting up the device, this commit validates it and if it is not compatible, it asks user whether he/she is okay with formatting or not. When the user confirms, SD card is formatted accordingly and the fresh SD card is ready to be used by BitBox02.