avr32: Add platform data for AC97C platform device

This patch adds platform data to the AC97C platform device. This will
let the board add a GPIO line which is connected to the external codecs
reset line.

The platform data, ac97c_platform_data, must also contain the DMA
controller ID, RX channel ID and TX channel ID.

Tested with Wolfson WM9712 and AP7000.

Signed-off-by: Hans-Christian Egtvedt <hcegtvedt@atmel.com>
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>