Implement support for SDIO/SDCard

[danielinux]

• as a block driver
• possibly starting from https://github.com/ChuckM/stm32f4-sdio-driver

[brabo]

There is also a stm32 SD driver for chans fatfs which Ken Sarkies ported to locm3 and made reentrant: http://jiggerjuice.info/electronics/projects/arm/chanfat-stm32f103-port.html