The Littlemill audio card supports a number of pluggable miniboards,
normally for the WM8994 family of devices. As all these devices look
mostly the same from an external configuration point of view and are
runtime enumerable we can write a standard machine driver which will
work out of the box with any of them. Start doing that with the bare
bones of a driver, only supporting AIF1.

Future patches will flesh this out to be more fully featured.
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>