Review and integrate downstream Teakra patches

[neobrain]

Some 3DS/DSi emulators that support audio maintain Teakra forks. We should review whether any of their modifications apply to Mikage as well. Any generic improvements should be upstreamed to Teakra itself so all emulators benefit from them.

Here's an incomplete list of specific patches to review:

• melonDS-emu/melonDS@31ba585 observed that some DSP firmware may trigger DMAs by writing to MMIO (0x2C6 + i * 0x80). Does this happen on 3DS, too?