seq: Add API functions to set different tempo base values

MIDI2 Set Tempo message uses 10ns-based values, and we need to update
the API to change the base time unit.

This patch adds a few new API functions:
- snd_seq_has_queue_tempo_base() returns 1 if the client supports a
  new tempo-base value; if 0, it's an old system and application has
  to use the tempo in the fixed 1us unit
- the tempo base can be changed with
  snd_seq_queue_tempo_set_tempo_base(), provided in nsec unit;
  the value has to be either 10 or 1000 (or 0 as default, equivalent
  with 1000)

The protocol version is checked and fallback to the fixed 1us base for
the old clients.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/uapi/asequencer.h

@@ -26,7 +26,7 @@
 #include <sound/asound.h>
 
 /** version of the sequencer */
-#define SNDRV_SEQ_VERSION SNDRV_PROTOCOL_VERSION(1, 0, 3)
+#define SNDRV_SEQ_VERSION SNDRV_PROTOCOL_VERSION(1, 0, 4)
 
 /**
  * definition of sequencer event types
@@ -539,11 +539,12 @@ struct snd_seq_queue_status {
 /* queue tempo */
 struct snd_seq_queue_tempo {
 	int queue;			/* sequencer queue */
-	unsigned int tempo;		/* current tempo, us/tick */
+	unsigned int tempo;		/* current tempo, us/tick (or different time-base below) */
 	int ppq;			/* time resolution, ticks/quarter */
 	unsigned int skew_value;	/* queue skew */
 	unsigned int skew_base;		/* queue skew base */
-	char reserved[24];		/* for the future */
+	unsigned short tempo_base;	/* tempo base in nsec unit; either 10 or 1000 */
+	char reserved[22];		/* for the future */
 };