ALSA: clean up the logic for building sequencer modules

Instead of mangling the CONFIG_* variables in the makefiles over and
over, set a few helper variables in Kconfig.

Signed-off-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/drivers/opl3/Makefile b/sound/drivers/opl3/Makefile
index 19767a6..7f2c2a1 100644
--- a/sound/drivers/opl3/Makefile
+++ b/sound/drivers/opl3/Makefile
@@ -7,14 +7,6 @@
 snd-opl3-synth-y := opl3_seq.o opl3_midi.o opl3_drums.o
 snd-opl3-synth-$(CONFIG_SND_SEQUENCER_OSS) += opl3_oss.o
 
-#
-# this function returns:
-#   "m" - CONFIG_SND_SEQUENCER is m
-#   <empty string> - CONFIG_SND_SEQUENCER is undefined
-#   otherwise parameter #1 value
-#
-sequencer = $(if $(subst y,,$(CONFIG_SND_SEQUENCER)),$(if $(1),m),$(if $(CONFIG_SND_SEQUENCER),$(1)))
-
 obj-$(CONFIG_SND_OPL3_LIB) += snd-opl3-lib.o
 obj-$(CONFIG_SND_OPL4_LIB) += snd-opl3-lib.o
-obj-$(call sequencer,$(CONFIG_SND_OPL3_LIB)) += snd-opl3-synth.o
+obj-$(CONFIG_SND_OPL3_LIB_SEQ) += snd-opl3-synth.o