Add modules/spi as a gathering point for SPI-related modules, analagous to

modules/i2c for i2c/iicbus modules.  Build spibus as a module.

sys/modules/Makefile

@@ -360,7 +360,7 @@ SUBDIR=	\
 	snp \
 	sound \
 	${_speaker} \
-	spigen \
+	spi \
 	${_splash} \
 	${_sppp} \
 	ste \

sys/modules/spi/Makefile

@@ -0,0 +1,7 @@
+# $FreeBSD$
+
+SUBDIR = \
+	../spigen \
+	spibus \
+	
+.include <bsd.subdir.mk>

sys/modules/spi/spibus/Makefile

@@ -0,0 +1,19 @@
+# $FreeBSD$
+
+.PATH:	${SRCTOP}/sys/dev/spibus
+
+KMOD=	spibus
+SRCS=	spibus.c
+
+.if !empty(OPT_FDT)
+SRCS+=	ofw_spibus.c
+.endif
+
+# Generated files...
+SRCS+=	\
+	bus_if.h \
+	device_if.h \
+	spibus_if.c \
+	spibus_if.h \
+
+.include <bsd.kmod.mk>