tools include UAPI: Sync sound/asound.h copy with the kernel sources

Picking the changes from:

  81be1093 ("ALSA: pcm: Add SNDRV_PCM_INFO_EXPLICIT_SYNC flag")

Which entails no changes in the tooling side as it doesn't introduce new
ioctls.

To silence this perf tools build warning:

  Warning: Kernel ABI header at 'tools/include/uapi/sound/asound.h' differs from latest version at 'include/uapi/sound/asound.h'
  diff -u tools/include/uapi/sound/asound.h include/uapi/sound/asound.h

Cc: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>