ALSA: ac97: Add helper function to reset the AC97 device

There is currently a lot of code duplication in ASoC drivers regarding the
reset handling of devices. This patch introduces a new generic reset
function in the generic AC'97 framework that can be used to replace most
the custom reset functions.

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