Since the build of PCM timer may be disabled via Kconfig now, each
driver that provides a timer interface needs to set CONFIG_SND_TIMER
explicitly.  Otherwise it may get a build error due to missing
symbol.

Fixes: 90bbaf66 ('ALSA: timer: add config item to export PCM timer disabling for expert')
Reported-by: Nkbuild test robot <fengguang.wu@intel.com>
Cc: <stable@vger.kernel.org> # v4.4+
Signed-off-by: NTakashi Iwai <tiwai@suse.de>