fdt: Add INT32_MAX to kernel.h for libfdt

Unfortunately libfdt needs this value now, which is present in the
stdint.h header. That file is just a placeholder in U-Boot and these sorts
of constants appear in the linux/kernel.h header instead.

To keep libfdt happy, add INT32_MAX too.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/include/linux/libfdt_env.h b/include/linux/libfdt_env.h
index e49fcd7..148b908 100644
--- a/include/linux/libfdt_env.h
+++ b/include/linux/libfdt_env.h
@@ -10,6 +10,7 @@
 #define LIBFDT_ENV_H
 
 #include <linux/string.h>
+#include <linux/kernel.h>
 
 #include <asm/byteorder.h>