ASoC: Move widgets from DAPM context to snd_soc_card

Decoupling widgets from DAPM context is required when extending the ASoC
core to cross-device paths. Even the list of widgets are now kept in
struct snd_soc_card, the widget listing in sysfs and debugs remain sorted
per device.

This patch makes possible to build cross-device paths but does not extend
yet the DAPM to handle codec bias and widget power changes of an another
device.

Cross-device paths are registered by listing the widgets from device A in
a map for device B. In case of conflicting widget names between the devices,
a uniform name prefix is needed to separate them. See commit ead9b919


"ASoC: Add optional name_prefix for kcontrol, widget and route names" for
help.

An example below shows a path that connects MONO out of A into Line In of B:

static const struct snd_soc_dapm_route mapA[] = {
	{"MONO", NULL, "DAC"},
};

static const struct snd_soc_dapm_route mapB[] = {
	{"Line In", NULL, "MONO"},
};

Signed-off-by: Jarkko Nikula <jhnikula@gmail.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>