fs: Move conditional compilation to Makefile

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/fs/fdos/Makefile b/fs/fdos/Makefile
index 2dba0fb..fce2032 100644
--- a/fs/fdos/Makefile
+++ b/fs/fdos/Makefile
@@ -31,10 +31,10 @@
 LIB	= $(obj)libfdos.a
 
 AOBJS	=
-COBJS	= fat.o vfat.o dev.o fdos.o fs.o subdir.o
+COBJS-$(CONFIG_CMD_FDOS) := fat.o vfat.o dev.o fdos.o fs.o subdir.o
 
-SRCS	:= $(AOBJS:.o=.S) $(COBJS:.o=.c)
-OBJS	:= $(addprefix $(obj),$(AOBJS) $(COBJS))
+SRCS	:= $(AOBJS:.o=.S) $(COBJS-y:.o=.c)
+OBJS	:= $(addprefix $(obj),$(AOBJS) $(COBJS-y))
 
 #CPPFLAGS +=