This also fixes#958
Original commits:
* initial work on cart save crypto/wearleveling
* add support for n3ds only save crypto
* use existing crc16 impl for save blockmap
* fix missing aeskey select for card2 save decrypt
* fix old/new cart media being swapped
* fix 1 MiB save chips / blockmap type 2
* move cart save wearleveling/crypto to separate file
* try 2nd wearlevel header on fail + minor fixes
* save_ctr: zero out savectx before reading fallback header
This is meant to replace the Prompt I was using previously.
Fun fact: WarioWare DIY seems to have *something* on the SPI bus, as it
returns an ID of 0x000001 consistently. Or am I just glitching the
parallel flash? Or did I get a fake?