[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>

sound/spi/Kconfig

@@ -0,0 +1,6 @@
+#SPI drivers
+
+menu "SPI devices"
+	depends on SND != n
+
+endmenu

sound/spi/Makefile

@@ -0,0 +1,2 @@
+# Makefile for SPI drivers
+