ipc4: mixin: Restore back gain support #17352

Job	Run time
build-windows (imx8 imx8x imx8m imx8ulp)	7m 46s
build-linux (mnfst, imx8 imx8x imx8m imx8ulp)	5m 16s
build-windows (mtl)	5m 57s
build-linux (mnfst, mtl)	4m 55s
LP64-WIP	3m 58s
build-linux (mnfst, lnl)	4m 23s
build-windows (tgl tgl-h)	7m 30s
build-windows (-d, mtl)	6m 42s
build-linux (mnfst, tgl tgl-h)	5m 20s
manifest-check	41s
build-linux (zmain, imx8 imx8x imx8m imx8ulp)	5m 7s
build-linux (zmain, mtl)	4m 28s
build-linux (zmain, lnl)	4m 22s
build-linux (zmain, tgl tgl-h)	5m 22s
build-linux (-d, mnfst, mtl)	4m 43s
compare-linux-win	44s
	1h 17m 14s

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