fusee: sdmmc: clean up and prepare for better SD/MMC/version separations

fusee: add support for SDMMC write operations

Fusee: fix typo

Fusee: Add #define requirement for pragmatic reasons.

fusee: enable sdmmc loglevel control

fusee: fix multiple-block SDMMC transfers

Move fatfs around

Initialize heap, increase stack size

Change defaut BCT0 for debug

Merge SD stuff into fusee-secondary. Switch diskio to single-sector reads temporarily

Push minimally working FATFS.

fusee: make SDMMC debug printing more manageable

fusee: get uSD working, fix bad no_iopower, and abstract card differences

fusee: fix SD pinmuxing / signal integrity issues

fusee: fix drive strength and avoid a pad wear-condition

fusee: merge in most of the microSD card (not fully working)

fusee: implement partition support; needs some tweeks

fusee: sdmmc: use v3 compatibility mode for it's simpler DMA ...

we may want to change this at some point to get 64-bit addressing?

fusee: sdmmc: support CPU reads in addition to (broken?) DMA

fusee: sdmmc: handle DMA page boundaries

sdmmc: mostly working for eMMC, now

fusee: get non-data SDMMC commands fully working on eMMC

fusee: further flesh out sdmmc implementation

fusee: fix issue with SDMMC psuedo-interrupts

fusee: add missing file

skeleton SDMMC

Fix small issues in the stage2 loader (#78) ...

* stage2 loader: Fix loadlist parsing breaking out of the loop too early

* stage2 loader: Use bct0 from the loader context

Change read_sd_file semantics to return size read.

Fusee: Fix BisPartition enum to correctly identify partitions. ...

* BisPartition_t was missing SAFE, meaning User and System were using wrong key_source

* Normalize tabs to spaces

* Merge User and System BisPartition_t because they are the same key anyway

* Remove extra newline

fusee: fix missing volatiles in memory utils