ASoC: davinci: Kconfig/Makefile: Generic EVM machine driver related cleanup

We have several boards using the same machine driver for audio support.
All of these machines can select a generic machine driver config option to
build the needed driver while keeping the config options used within the
driver for compile time code path selection.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>