[stm32f7] Add support for stm32f7 microcontrollers

Updated features:

• SD card driver
• Backup domain driver (old Safe-Guard-Memory)
• 767 Nucleo, 769 Discovery and Skyward's Compute Unit boards support
• Added V_DDA_VOLTAGE macro on most boards to specify the analog supply voltage
• Fixed wrong sd card voltages on some Skyward's boards