[ALSA] ASoC pxa2xx DMA support

This patch adds pxa2xx ASoC DMA audio support. It's based on
sound/arm/pxa-pcm.c by Nicolas Pitre with the following differences.
o Modified driver structure to use ASoC core PCM callbacks and data
structures.
o Registration with ASoC core.
From: Liam Girdwood <liam.girdwood@wolfsonmicro.com>
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Liam Girdwood <liam.girdwood@wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>