ALSA: emu10k1: add synchronized start of multi-channel playback

We use independent voices for the channels, so we need to make an effort
to ensure that they are actually in sync.

The hardware doesn't provide atomicity, so we may need to retry a few
times, due to NMIs, PCI contention, and the wrong phase of the moon.

Solution inspired by kX-project.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230523200709.236023-3-oswald.buddenhagen@gmx.de


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