[ALSA] snd-powermac: handle dead DMA transfers

This patch provides the snd-powermac sound driver with the ability to handle
dead DMA transfers. If a dead DMA transfer is detected, the driver now sets
up a new DMA transfer to continue with the sound output at the point where the
old transfer died.
This dead DMA transfer handling has become necessary with recent kernels on
certain G4 PowerMacs. Please refer to the following URLs for more information:
 https://bugtrack.alsa-project.org/alsa-bug/view.php?id=3126
 https://bugs.launchpad.net/ubuntu/+source/linux-source-2.6.20/+bug/87652
 http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=436723
The patch is based on the dead DMA transfer handling code from the old dmasound
driver which can be found in the file sound/oss/dmasound/dmasound_awacs.c in
the Linux source code.

Signed-off-by: T. H. Huth <th.huth@googlemail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>