ALSA: AC97: add AC97 support for AT91.

This patch add AC97 support for ATMEL AT91, using the AVR32 code.
While AVR is using a DMA, the AT91 chips are using a Peripheral Data
Controller.

Signed-off-by: Sedji Gaouaou <sedji.gaouaou@atmel.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>