libeffects: Added standalone testbench that calculates SNR value

Added a standalone test bench that calculates SNR values using 2 files
as input. This tool is used to test the multichannel changes.

Test: build_and_run_all_unit_tests.sh
Bug: 121353611
Change-Id: I5e67d8113bace7872133f2e02d9ae7b9d90e61ff
3 files changed