SDIO library for the STM32L476RG MCU.

• Card initialization (SDSCv1, SDSCv2, SDHC, SDXC, partial MMC)
• Read: polling or DMA, single or multiple block
• Write: polling or DMA, single or multiple block

Ported from L1 series, still needs some optimizations and polish.

main.c contains code to test performance of read and write operations, pretty stupid, but it works.

Note: should work on all STM32L4 MCUs but not the STM32L4+