ASoC: Shutdown DAPM contexts when removing a card

Currently when a ASoC sound card is unregistered we leave the individual
components in their current state, just call the remove() callback and leave
it to the drivers to do the proper shutdown/cleanup.

This patch introduces a call to snd_soc_dapm_shutdown() when removing the
card.  This will make sure that all DAPM widgets are properly powered down
and all DAPM contexts are put at the SND_SOC_BIAS_OFF level. This will
ensure that all components are properly powered down when the card is
removed.

Since a lot of drivers manually go to SND_SOC_BIAS_OFF in their remove
callback this will also allow us to remove a bit of duplicated code.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>