techpack: audio: Construct and add audio techpack Kconfig to build

This is the only way to solve the mess that happens whenever
we try to rebuild the kernel without mrproper'ing it first.

It's the most dirty thing on Earth, but it's really the only
possible option.

Change-Id: Ie72adbb63d8c0a9c2d53cd4a9e8610ad9ccfef9b