seq: Add API functions to set different tempo base values

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>