ALSA: Add SoC on-chip internal ram support for DMA buffer allocation

Now it's quite common that an SoC contains its on-chip internal RAM.
By using this RAM space for DMA buffer during audio playback/record,
we can shutdown the voltage for external RAM to save power.

So add new DEV type with iram malloc()/free() and accordingly modify
current default mmap() for the iram circumstance.

Signed-off-by: Nicolin Chen <b42378@freescale.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/memalloc.h

@@ -52,6 +52,7 @@ struct snd_dma_device {
 #else
 #define SNDRV_DMA_TYPE_DEV_SG	SNDRV_DMA_TYPE_DEV /* no SG-buf support */
 #endif
+#define SNDRV_DMA_TYPE_DEV_IRAM		4	/* generic device iram-buffer */
 
 /*
  * info for buffer allocation