The PCM x-fi native update routine can cause deadlocks when the
trigger(START) is called while the stream is running.

This patch fixes the deadlock by just postponing the pcm period update
to the next possible wake-up.  Also it adds the flip of ti->running
flag (just to be sure as now).
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

Added use_system_timer module option to force to use the system timer
instead of emu20k1 timer irq for debugging.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

Optimize the timer update routine to look up wall clock once instead of
checking the position of each stream at each timer update.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

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

emu20k1 has a native timer interrupt based on the audio clock, which
is more accurate than the system timer (from the synchronization POV).
This patch adds the code to handle this with multiple streams.

The system timer is still used on emu20k2, and can be used also for
emu20k1 easily by changing USE_SYSTEM_TIMER to 1 in cttimer.c.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>