ALSA: Add a note on dependency of RTC stuff

Added a note on the dependency of old RTC stuff, which is exclusive
with the new RTC class drivers.
    http://bugme.linux-foundation.org/show_bug.cgi?id=11430Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NJaroslav Kysela <perex@perex.cz>

sound/core/Kconfig

@@ -108,6 +108,9 @@ config SND_RTCTIMER
 	  To compile this driver as a module, choose M here: the module
 	  will be called snd-rtctimer.
 
+	  Note that this option is exclusive with the new RTC drivers
+	  (CONFIG_RTC_CLASS) since this requires the old API.
+
 config SND_SEQ_RTCTIMER_DEFAULT
 	bool "Use RTC as default sequencer timer"
 	depends on SND_RTCTIMER && SND_SEQUENCER