libfdt: split fdt_region declarations out to <fdt_region.h>

fdt_region APIs are not part of libfdt. They are U-Boot extension
for the verified boot. Split the declarations related to fdt_region
out of <fdt_region.h>. This allows <linux/libfdt.h> to become a
simple wrapper file, like Linux does.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
diff --git a/common/image-fit-sig.c b/common/image-fit-sig.c
index 490566c..3e73578 100644
--- a/common/image-fit-sig.c
+++ b/common/image-fit-sig.c
@@ -11,6 +11,7 @@
 #include <malloc.h>
 DECLARE_GLOBAL_DATA_PTR;
 #endif /* !USE_HOSTCC*/
+#include <fdt_region.h>
 #include <image.h>
 #include <u-boot/rsa.h>
 #include <u-boot/rsa-checksum.h>