Merge "audio: add 'useForVolume' field to 'gain'." into android10-tests-dev am: 864312809f am: ca7275a3d8

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/1161727

Change-Id: Ic81dc4d85961fa449f6f2e8fecb1ddceec642704