ALSA: hdspm - Add support for AEBs on RME AIO

AIO cards allow to use AEB (Analogue Expansion Boards) to add four
input and/or output channels.

This patch adds the necessary code to detect and enable the additional
I/O channels.

Signed-off-by: Adrian Knoth <adi@drcomp.erfurt.thur.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>