libfdt: move CONFIG_OF_LIBFDT and CONFIG_FIT to lib/Makefile

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/lib/libfdt/Makefile b/lib/libfdt/Makefile
index 6fe79e0..2f5413f 100644
--- a/lib/libfdt/Makefile
+++ b/lib/libfdt/Makefile
@@ -5,8 +5,5 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-COBJS-libfdt += fdt.o fdt_ro.o fdt_rw.o fdt_strerror.o fdt_sw.o fdt_wip.o \
+obj-y += fdt.o fdt_ro.o fdt_rw.o fdt_strerror.o fdt_sw.o fdt_wip.o \
 	fdt_empty_tree.o fdt_addresses.o
-
-obj-$(CONFIG_OF_LIBFDT) += $(COBJS-libfdt)
-obj-$(CONFIG_FIT) += $(COBJS-libfdt)