fdt: Allow FDT functions to be built for SPL

Remove the implicit assumption that SPL does not support device tree.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/Makefile b/lib/Makefile
index 07d175f..97ed398 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -44,6 +44,12 @@
 obj-y += list_sort.o
 endif
 
+ifndef CONFIG_SPL_DISABLE_OF_CONTROL
+obj-$(CONFIG_OF_LIBFDT) += libfdt/
+obj-$(CONFIG_OF_CONTROL) += fdtdec_common.o
+obj-$(CONFIG_OF_CONTROL) += fdtdec.o
+endif
+
 ifdef CONFIG_SPL_BUILD
 obj-$(CONFIG_SPL_YMODEM_SUPPORT) += crc16.o
 obj-$(CONFIG_SPL_NET_SUPPORT) += net_utils.o