gcc 10 no longer lets you get away with not externing global variables in header files. This adds the necessary extern and adds defines in appropriate c files
hekate main always runs in compatibility mode (SDR82).
This ensures speed on boot process.
Nyx will first try SDR104.
If the sd card is a sandisk U1 and fails, it will try the compatibility mode.
After that it fallbacks to lower bus speeds.
Both support 1bit mode for broken sd card readers.
Having the new error checking in the sdmmc driver, allows for all that to work.
It can now fail instead of continuing, like how HOS reacts.
