drivers: convert makefiles to Kbuild style

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/drivers/dfu/Makefile b/drivers/dfu/Makefile
index de9e44e..def628d 100644
--- a/drivers/dfu/Makefile
+++ b/drivers/dfu/Makefile
@@ -5,26 +5,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
-
-LIB	= $(obj)libdfu.o
-
-COBJS-$(CONFIG_DFU_FUNCTION) += dfu.o
-COBJS-$(CONFIG_DFU_MMC) += dfu_mmc.o
-COBJS-$(CONFIG_DFU_NAND) += dfu_nand.o
-COBJS-$(CONFIG_DFU_RAM) += dfu_ram.o
-
-SRCS    := $(COBJS-y:.o=.c)
-OBJS	:= $(addprefix $(obj),$(COBJS-y))
-
-$(LIB):	$(obj).depend $(OBJS)
-	$(call cmd_link_o_target, $(OBJS))
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-#########################################################################
+obj-$(CONFIG_DFU_FUNCTION) += dfu.o
+obj-$(CONFIG_DFU_MMC) += dfu_mmc.o
+obj-$(CONFIG_DFU_NAND) += dfu_nand.o
+obj-$(CONFIG_DFU_RAM) += dfu_ram.o