EffectDownmix: Use full 22.2 matrix

Update to use a full 22.2 downmix matrix, where
coefficients beyond 7.1 are based on
ARIB STD-B32 22.2 Downmix Coefficients.

See:

Downmixing Method for 22.2 Multichannel Sound Signal in
8K Super Hi-Vision Broadcasting,
Takehiro Sugimoto, Satoshi Oode, and Yasushige Nakayama,
Journal of the Audio Engineering Society ENGINEERING REPORTS
Vol. 63, No. 7/8, July/August 2015, p 590 - 599.

Test: downmix_benchmark
Test: downmix_tests
Bug: 188502620
Bug: 189336830
Change-Id: I63cd4f12134f9315e253ffd21a8c2d6e43371db8