lib: convert makefiles to Kbuild style

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/lib/libfdt/Makefile b/lib/libfdt/Makefile
index 07373df..a02c9b0 100644
--- a/lib/libfdt/Makefile
+++ b/lib/libfdt/Makefile
@@ -5,30 +5,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
-
-LIB	= $(obj)libfdt.o
-
-SOBJS	=
-
 COBJS-libfdt += fdt.o fdt_ro.o fdt_rw.o fdt_strerror.o fdt_sw.o fdt_wip.o fdt_empty_tree.o
 
-COBJS-$(CONFIG_OF_LIBFDT) += $(COBJS-libfdt)
-COBJS-$(CONFIG_FIT) += $(COBJS-libfdt)
-
-
-COBJS	:= $(sort $(COBJS-y))
-SRCS	:= $(SOBJS:.o=.S) $(COBJS:.o=.c)
-OBJS	:= $(addprefix $(obj),$(SOBJS) $(COBJS))
-
-$(LIB):	$(obj).depend $(OBJS)
-	$(call cmd_link_o_target, $(OBJS))
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
-
-#########################################################################
+obj-$(CONFIG_OF_LIBFDT) += $(COBJS-libfdt)
+obj-$(CONFIG_FIT) += $(COBJS-libfdt)