ALSA: Add ALSA driver for Atmel AC97 controller

This patch adds ALSA support for the AC97 controller found on Atmel
AVR32 devices.

Tested on ATSTK1006 + ATSTK1000 with a development board with a AC97
codec.

Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>