This commit:
* Adds a new subproject, audio_core.
* Defines structures that exist in DSP shared memory.
* Hooks up various other parts of the emulator into audio core.
This sets the foundation for a later HLE DSP implementation.
This adds some structures necessary to support multiple memory regions
in the future. It also adds support for different system memory types
and the new linear heap mapping at 0x30000000.