ALSA: pcm - Export snd_pcm_lib_default_mmap() helper

Export the default mmap function, snd_pcm_lib_default_mmap().
The upcoming non-snooping support in HD-audio driver will use this
to override the mmap method.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 57e71fa..249d988 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -1035,6 +1035,8 @@
 	atomic_dec(&substream->mmap_count);
 }
 
+int snd_pcm_lib_default_mmap(struct snd_pcm_substream *substream,
+			     struct vm_area_struct *area);
 /* mmap for io-memory area */
 #if defined(CONFIG_X86) || defined(CONFIG_PPC) || defined(CONFIG_ALPHA)
 #define SNDRV_PCM_INFO_MMAP_IOMEM	SNDRV_PCM_INFO_MMAP