ALSA: atmel: Remove AVR32 bits from the driver

AVR32 is gone. Now it's time to clean up the driver by removing
leftovers that was used by AVR32 related code.

Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>