Nitpick: Correct RNG state pointer type in the noise oscillator
Moved compile time configuration definitions into config.h

Also figured out why the RNG/noise cleanup commit mysteriously
gave much worse benchmark results: wtosc.c was compiled with
A2_HIFI undefined! We've been running linear interpolation with
2x oversampling for quite some time.

The good news is, LERP 2x is fast and surprisingly good with
mipmapped waves!

New benchmark of 65505c25104700f36d59cad65bf20019c8a5fa86.
Results for "normal" quality (LERP 2x) are mostly identical,
so no obvious breakage. A2_LOFI is only marginally faster
(which makes it quite pointless, as mipmapping is practically
broken without the 2x oversampling), whereas A2_HIFI is
substantially slower.