ALSA: Fix SG-buffer DMA with non-coherent architectures

Using SG-buffers with dma_alloc_coherent() is often very inefficient
on non-coherent architectures because a tracking record could be
allocated in addition for each dma_alloc_coherent() call.
Instead, simply disable SG-buffers but just allocate normal continuous
buffers on non-supported (currently all but x86) architectures.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/core/Kconfig b/sound/core/Kconfig
index 6061fb5..c15682a 100644
--- a/sound/core/Kconfig
+++ b/sound/core/Kconfig
@@ -206,4 +206,8 @@
 config SND_VMASTER
 	bool
 
+config SND_DMA_SGBUF
+	def_bool y
+	depends on X86
+
 source "sound/core/seq/Kconfig"