[opus] ARM NEON optimization -- celt_fir()

[Timothy B. Terriberry]

Jonathan Lennox wrote:
> Hi, Linfeng —
>
> Please note the aarch64 optimization patches I submitted in November and December (which Tim still hasn’t gotten around to reviewing).  As they used Neon intrinsics, several of these actually applied to both armv7 and aarch64 Neon.

Yes, it seems I need to move this up my priority list to avoid everyone 
wasting time on duplicate work. Fortunately, I have a long plane flight 
tomorrow...

If you have any comments on Jonathan's patches (any of them), Linfeng, 
that would also be good to know.