ALSA: timer: add config item to export PCM timer disabling for expert

PCM timer is not always used. For embedded device, we need an interface
to disable it when it is not needed, to shrink the kernel size and
memory footprint, here add CONFIG_SND_PCM_TIMER for it.

When both CONFIG_SND_PCM_TIMER and CONFIG_SND_TIMER is unselected,
about 25KB saving bonus we can get.

Please be noted that when disabled, those stubs who using pcm timer
(e.g. dmix, dsnoop & co) may work incorrectlly.

Suggested-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jie Yang <yang.jie@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/core/Kconfig b/sound/core/Kconfig
index 6c96fee..e3e9491 100644
--- a/sound/core/Kconfig
+++ b/sound/core/Kconfig
@@ -4,7 +4,7 @@
 
 config SND_PCM
 	tristate
-	select SND_TIMER
+	select SND_TIMER if SND_PCM_TIMER
 
 config SND_PCM_ELD
 	bool
@@ -93,6 +93,17 @@
           support conversion of channels, formats and rates. It will
           behave like most of new OSS/Free drivers in 2.4/2.6 kernels.
 
+config SND_PCM_TIMER
+	bool "PCM timer interface" if EXPERT
+	default y
+	help
+	  If you disable this option, pcm timer will be inavailable, so
+	  those stubs used pcm timer (e.g. dmix, dsnoop & co) may work
+	  incorrectlly.
+
+	  For some embedded device, we may disable it to reduce memory
+	  footprint, about 20KB on x86_64 platform.
+
 config SND_SEQUENCER_OSS
 	bool "OSS Sequencer API"
 	depends on SND_SEQUENCER