[opus] [Aarch64 v2 05/18] Add Neon intrinsics for Silk noise shape quantization.

[Timothy B. Terriberry]

Jonathan Lennox wrote:
> Would something like an OPUS_ARCH_ARM_NEON #define in celt/arm/armcpu.h be okay?  It’d be a bit confusing with OPUS_CPU_ARM_NEON in armcpu.c, but I could probably organize it to be sensible.

Yes, this is what I had in mind. I would have suggested just replacing 
the existing constants in armcpu.c (either just do the shifts manually, 
or have some sort of _FLAG variant that encapsulates the shift).