The board layer does not work for SDIO

[jkrech]

SDIO problem:

• CubeMX creates 'HAL_SD_ConfigWideBusOperation(&hsd, SDIO_BUS_WIDE_4B)' function call in main.c. This function call returns always with error but I was not able to find the reason.
• Currently the call is commented out to make the layer run successfully.
• Once CbeMX generator is invoked again this manual change will be overwritten

uSD Card Detect pin (PG2)

• Pin is configured but not listed in MX_Device.h -> @DavidLesnjak does this require a change in the cbridge?

[VladimirUmek]

SDIO problem:
This is configuration issue. I checked driver documentation and it did not mention that MX_*_SD_Init function shall not be called in main.c. Therefore this commit adds brief description what to do and example (in the same doc page) shows the steps.

uSD Card Detect:
An arbitrary GPIO pin can be configured as Card Detect pin and User Label MemoryCard_n_CD (n is peripheral instance number) must be added to it in STM32CubeMX. Define is generated in main.h which is included in MCI driver implementation. MCI driver then uses generated defines to read pin state.