Add SIMD NEON Optimization for QT_FP16 in Scalar Quantizer (facebookr…

…esearch#3166)

Summary:
### Description
We have SIMD support for x86 architecture using AVX2 optimization. But, we don't have a similar optimization for ARM architecture in Scalar Quantizer for the Quantization Type `QT_FP16`. This PR adds SIMD support for ARM using NEON optimization.

### Issues resolved
facebookresearch#3014

Pull Request resolved: facebookresearch#3166

Reviewed By: algoriddle, pemazare

Differential Revision: D52510486

Pulled By: mdouze

fbshipit-source-id: 2bb360475a0d9e0816c8e05b44d7da7f2e6b28c5

faiss/CMakeLists.txt

@@ -189,6 +189,7 @@ set(FAISS_HEADERS
   utils/extra_distances.h
   utils/fp16-fp16c.h
   utils/fp16-inl.h
+  utils/fp16-arm.h
   utils/fp16.h
   utils/hamming-inl.h
   utils/hamming.h