[ALSA] Add SPI devices to ALSA Kconfig and Makefile

This patch adds SPI devices in the ALSA diretory, including the Kconfig and
Makefile.

Signed-off-by: Hans-Christian Egtvedt <hcegtvedt@atmel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>
diff --git a/sound/spi/Makefile b/sound/spi/Makefile
new file mode 100644
index 0000000..30d8ec9
--- /dev/null
+++ b/sound/spi/Makefile
@@ -0,0 +1,2 @@
+# Makefile for SPI drivers
+