Most of the complex functionality in AEC3 is done using
vector maths. This CL adds a new functionality for
performing these using SIMD operations in a simple manner
whenever such are available.
The reason for putting the implementations in the header file
is to allow any possible inlining.
BUG=webrtc:6018
Review-Url: https://codereview.webrtc.org/2813823002
Cr-Commit-Position: refs/heads/master@{#17663}
