ALSA: pcm: Avoid mmap warnings on x86

On x86, using dma_mmap_coherent() for the pages allocated via
dma_alloc_coherent() results in a warning like:
  aplay:32536 map pfn RAM range req uncached-minus for [mem 0x21d500000-0x21d51ffff], got write-back

Until the issue is addressed in the core side, take back to the old
good way in PCM code only for x86.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_native.c

@@ -3326,6 +3326,7 @@ int snd_pcm_lib_default_mmap(struct snd_pcm_substream *substream,
 				area->vm_end - area->vm_start, area->vm_page_prot);
 	}
 #endif /* CONFIG_GENERIC_ALLOCATOR */
+#ifndef CONFIG_X86 /* for avoiding warnings arch/x86/mm/pat.c */
 	if (!substream->ops->page &&
 	    substream->dma_buffer.dev.type == SNDRV_DMA_TYPE_DEV)
 		return dma_mmap_coherent(substream->dma_buffer.dev.dev,
@@ -3333,6 +3334,7 @@ int snd_pcm_lib_default_mmap(struct snd_pcm_substream *substream,
 					 substream->runtime->dma_area,
 					 substream->runtime->dma_addr,
 					 area->vm_end - area->vm_start);
+#endif /* CONFIG_X86 */
 	/* mmap with fault handler */
 	area->vm_ops = &snd_pcm_vm_ops_data_fault;
 	return 0;