[ALSA] PCM interface - rename SNDRV_PCM_TSTAMP_MMAP to SNDRV_PCM_TSTAMP_ENABLE

Change semantics for SNDRV_PCM_TSTAMP_MMAP. Doing timestamping only in
the interrupt handler might cause that hw_ptr is not related to actual
timestamp. With this change, grab timestamp at every hw_ptr update to
have always valid timestamp + ring buffer position pair.
With this change, SNDRV_PCM_TSTAMP_MMAP was renamed to
SNDRV_PCM_TSTAMP_ENABLE. It's no regression (I think).

Signed-off-by: Jaroslav Kysela <perex@perex.cz>
diff --git a/include/sound/asound.h b/include/sound/asound.h
index 069d912..3eaf155 100644
--- a/include/sound/asound.h
+++ b/include/sound/asound.h
@@ -354,8 +354,8 @@
 
 enum {
 	SNDRV_PCM_TSTAMP_NONE = 0,
-	SNDRV_PCM_TSTAMP_MMAP,
-	SNDRV_PCM_TSTAMP_LAST = SNDRV_PCM_TSTAMP_MMAP,
+	SNDRV_PCM_TSTAMP_ENABLE,
+	SNDRV_PCM_TSTAMP_LAST = SNDRV_PCM_TSTAMP_ENABLE,
 };
 
 struct snd_pcm_sw_params {