The equalizer is implemented using a chain of biquads. Each biquad can
be lowpass, highpass, peaking, etc. The biquad formula is ported from
Chromium browser.

BUG=chromium:220340
TEST=make check; run eq_test and plot_fftl.m and verify.
Change-Id: I80a3df15155589e006275911ec58cfde7020ccbb
Reviewed-on: https://gerrit.chromium.org/gerrit/57584


Reviewed-by: Dylan Reid <dgreid@chromium.org>
Commit-Queue: Chih-Chung Chang <chihchung@chromium.org>
Tested-by: Chih-Chung Chang <chihchung@chromium.org>