DSP: Fix write masks on AUDIO_*/AR_* MMIO registers

[smurf3tte]

https://bugs.dolphin-emu.org/issues/6749

This change fixes the scratchy audio in Teenage Mutant Ninja Turtles (SX7E52/SX7P52). The game starts an audio interface DMA with an unaligned address, and because Dolphin was not masking off the low 5 bits of AUDIO_DMA_START_LO, all future AI DMAs were misaligned. To understand why, it is instructive to refer to AUDIO_InitDMA() in libogc, which behaves the same as the official SDK:

_dspReg[25] = (_dspReg[25]&~0xffe0)|(startaddr&0xffff);

The implementation does not mask off the low bits of the passed in value before it ORs them with low bits of the current register value. Therefore, if they are not masked off by the hardware itself, they become permanently stuck once set.

Adding a write mask for AUDIO_DMA_START_LO is enough to fix the bug in TMNT, but I decided to run some tests on GC and Wii to find the correct write masks for the surrounding registers, as only a couple were already being masked. Dolphin has gotten away with not masking the rest because many are already A) masked on read (or never read) by the SDK and/or B) masked on use (or never used) in Dolphin.

This leaves just three registers where the difference may be observable: AR_DMA_CNT_H and AUDIO_DMA_START_HI/LO.

[JMC47]

Fixes The Bachelor for Wii as well.

[BhaaLseN]

Code looks good, untested

[Silanda]

It looks like this fixes Dragon's Lair Trilogy too: https://bugs.dolphin-emu.org/issues/12349

[delroth]

LGTM, configmed with @smurf3tte that this was hardware tested and that the register masking does happen when writing and not in the DMA engine itself.