CODEC driver

[Wolfvak]

Currently there's a single "codec" device connected via the SPI bus and it controls touchscreen and circlepad stuff. In reality this driver also controls other registers responsible for sound (https://problemkaputt.de/gbatek.htm#3dstscregistersummary) and works similarly to the MCU or any other mfd, so it needs to be split off. However, the codec driver is also the one responsible for managing the swkbd which is pretty essential.

We need something like wifi or infrared to have proper communications with the system while debugging it (there are no UART ports exposed) before we can even think about ripping out swkbd and splitting the codec driver.

Marking as blocked by #6

[profi200]

"Reference" implementation:
https://github.com/profi200/open_agb_firm/blob/kernel_experiments/source/arm11/hardware/codec.c

It's a dumpster fire but that's to be expected with reverse engineered code i didn't have time to clean up yet.

[Wolfvak]

Yup, its listed in the wiki as such https://github.com/linux-3ds/linux/wiki/Driver-and-platform-support#spi-subdevices