Add vectorized implementation of nsse16 function.

Performance comparison tests are shown below.
- nsse_0_c: 682.2
- nsse_0_neon: 116.5

Benchmarks and tests run with checkasm tool on AWS Graviton 3.
Co-authored-by: Martin Storsjö <martin@martin.st>
Signed-off-by: Hubert Mazur <hum@semihalf.com>
Signed-off-by: Martin Storsjö <martin@martin.st>