STM32SD end() functionality to support SD card/library reset during operation

[BrynMorgan1]

The current STM32SD library does not have an end() or similar function to support stopping and deinitialising the library and SDIO peripheral.

Having an end() function would allow for:

• SD card reinsertion without resetting the MCU
• SDIO peripheral reset in rare case of SD card hang/fault

The end() function should perform the following at least:

• Deinitialise the SDIO peripheral of the MCU
• Reset the STM32SD library to an uninitialised state, such that begin() may be called again successfully
• Allow the SDIO GPIO pins to be configured as normal GPIO pins (eg. configured as analog input to save power in low-power state)

The Arduino SD library has recently implemented support for end(), which looks like this:
https://github.com/arduino-libraries/SD/blob/a3866205cf9af4eea3e10dcdc5ac2c713f293337/src/SD.cpp#L369-L372

Kind regards,
Bryn

[fpistm]

For ref: arduino-libraries/SD#37