ASoC: add snd_soc_of_parse_audio_simple_widgets for DT

This patch adds snd_soc_of_parse_audio_simple_widgets() and supports
below style of widgets name on DT:

	"template-wname", "user supplied wname"

For instance:
	simple-audio-widgets =
		"Microphone", "Microphone Jack",
		"Line", "Line In Jack",
		"Line", "Line Out Jack",
		"Headphone", "Headphone Jack",
		"Speaker", "Speaker External";

The "template-wname" currently includes: "Microphone", "Line", "Headphone"
and "Speaker".

Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>