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>
diff --git a/board/BuR/brxre1/board.c b/board/BuR/brxre1/board.c
index 0d1c6c4..873208c 100644
--- a/board/BuR/brxre1/board.c
+++ b/board/BuR/brxre1/board.c
@@ -9,6 +9,7 @@
  *
  */
 #include <common.h>
+#include <env.h>
 #include <errno.h>
 #include <spl.h>
 #include <asm/arch/cpu.h>