ALSA: Make CONFIG_SND_OSSEMUL user-selectable

Currently CONFIG_SND_OSSEMUL is selected by each config like
CONFIG_SND_PCM_OSS.  But, as see in the raw MIDI code that is built
conditionally with CONFIG_SND_OSSEMUL, we should rather make
CONFIG_SND_OSSEMUL user-selectable as the top kconfig item, and leave
the rest depending on it.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/Kconfig

@@ -59,12 +59,14 @@ config SND_SEQ_DUMMY
 	  will be called snd-seq-dummy.
 
 config SND_OSSEMUL
+	bool "Enable OSS Emulation"
 	select SOUND_OSS_CORE
-	bool
+	help
+	  This option enables the build of OSS emulation layer.
 
 config SND_MIXER_OSS
 	tristate "OSS Mixer API"
-	select SND_OSSEMUL
+	depends on SND_OSSEMUL
 	help
 	  To enable OSS mixer API emulation (/dev/mixer*), say Y here
 	  and read <file:Documentation/sound/alsa/OSS-Emulation.txt>.
@@ -76,7 +78,7 @@ config SND_MIXER_OSS
 
 config SND_PCM_OSS
 	tristate "OSS PCM (digital audio) API"
-	select SND_OSSEMUL
+	depends on SND_OSSEMUL
 	select SND_PCM
 	help
 	  To enable OSS digital audio (PCM) emulation (/dev/dsp*), say Y
@@ -110,7 +112,7 @@ config SND_PCM_TIMER
 config SND_SEQUENCER_OSS
 	bool "OSS Sequencer API"
 	depends on SND_SEQUENCER
-	select SND_OSSEMUL
+	depends on SND_OSSEMUL
 	help
 	  Say Y here to enable OSS sequencer emulation (both
 	  /dev/sequencer and /dev/music interfaces).