env: Move env_get_ulong() to env.h

Move env_get_ulong() over to the new header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

lib/fdtdec.c

@@ -8,6 +8,7 @@
 #include <boot_fit.h>
 #include <dm.h>
 #include <dm/of_extra.h>
+#include <env.h>
 #include <errno.h>
 #include <fdtdec.h>
 #include <fdt_support.h>